NOVELTY - A hydrogen-generating device comprises: (i) a reforming portion; (ii) a supply portion; (iii) a hydrogen separating portion having a hydrogen separating membrane, and reformed gas and hydrogen flow passages; and (iv) a hydrogen suppressing portion for suppressing hydrogen concentration in the reformed gas supplied to hydrogen separating membrane in a low-temperature condition.    USE - For generating hydrogen-rich gas by reforming raw material.    ADVANTAGE - Hydrogen embrittlement of hydrogen separating membrane in low-temperature condition is suppressed. Thermal stress during the warm-up operation of hydrogen generating is suppressed, and generation of cracks and damages on hydrogen separating membrane is reduced.    DETAILED DESCRIPTION - A hydrogen-generating device consists of reforming portion, supply portion, hydrogen separating portion, and hydrogen suppressing portion. The reforming portion generates reformed gas by reforming the raw material. The supply portion supplies a substance required for reforming to the reforming portion. The hydrogen separating portion has a hydrogen separating membrane for selectively permeating hydrogen, and reformed gas and hydrogen flow passages arranged to sandwich the hydrogen separating membrane. The hydrogen separating portion separates hydrogen towards the hydrogen flow passage side from the reformed gas supplied to the reformed gas flow passage. The hydrogen suppressing portion suppresses hydrogen concentration in the reformed gas supplied to the reformed gas flow passage in a low-temperature condition where a temperature of hydrogen separating portion is lower than a predetermined value which is determined based on a material of hydrogen separating membrane.    An INDEPENDENT CLAIM is also included for a control method for hydrogen generating device, including suppressing hydrogen concentration in the reformed gas supplied to the hydrogen separating membrane when the hydrogen-generating device is in low temperature condition.    DESCRIPTION OF DRAWING(S) - The figure is an explanatory view of a sequence of e.g. an amount of oxygen in the starting control process.