NOVELTY - An ethylene gas is modified by irradiating ultra-violet rays with a wavelength of 254 nm toward the water droplets held on water retention surface from a near distance within 10 mm while controlling its nearby temperature at 10-40degreesC; and aerating gas containing ethylene gas to the water retention surface to contact the ethylene gas with the OH radical.    USE - For modifying ethylene gas.    ADVANTAGE - The invention eliminates the difficulty found in countermeasure against ethylene gas through a plasma discharging in the prior art, shows less consumption power, and modifies ethylene gas harmful against keeping the freshness released from the agricultural product into the storehouse and keeping the freshness of the fresh agricultural product for a long period of time.    DETAILED DESCRIPTION - Modification of an ethylene gas involves retaining water by supplying water to a water retention member formed with a water retention surface capable of holding water in particle form at its surface and holding the water retention surface in a state wetted by water droplets (M); irradiating the ultra-violet rays with a wavelength of 254 nm toward the water droplets held on the water retention surface from a near distance within 10 mm while controlling its nearby temperature at 10-40degreesC to generate hydroxide (OH) radical in the water droplets with an energy of the irradiated ultra-violet rays; and aerating gas containing ethylene gas to the water retention surface holding the water droplets containing the OH radical to contact the ethylene gas with the OH radical. The ethylene gas is contacted and reacted with the OH radical through each of the steps to enable it to be modified into ethane (e) and water (w).    INDEPENDENT CLAIMS are also included for:    (1) an ethylene gas modifying device for carrying out the ethylene gas modifying method comprising a water retention member made of material having a water repelling characteristic to form a water retention surface (2a) capable of holding water in particle form at the surface; ultra-violet rays generating tube (3) for generating ultra-violet rays with a wavelength of 254 nm arranged in a near distance within 10 mm toward the water retention surface; a temperature control mechanism for controlling a location near the irradiated ultra-violet rays in 10-40degreesC; a water holding mechanism for holding water in a particle form on the water retention surface; and aeration mechanism for passing gas containing ethylene gas to make contact with the water droplets held on the water retention surface; and    (2) a freshness keeping device for a fresh agricultural product, comprising the ethylene gas modifying device installed in a storehouse for use in storing the fresh agricultural product. Gas in the storehouse is circulated through the aeration mechanism of the ethylene gas modifying device. The ethylene gas generated from the agricultural product stored in the storehouse is contacted and reacted with OH radical generated through irradiation of ultra-violet rays and held on the water retention surface to modify it into harmless ethane and water, thus harmful ethylene gas in the storehouse is reduced and the freshness of the fresh agricultural product can be kept for a long period of time.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic side elevation view in longitudinal section of the device.    Surface (2a)    Ultra-violet rays generating tube (3)    Electrical heating heater (29)    Ethane (e)    Water droplets (M)    Water (w)