NOVELTY - A tidal current and ocean current electric power generation system (1) has an electric power generation unit (10), an electric power generation state detector (40) to sense the flow of seawater, a state switch (50) to adjust the output state of the electric power generation unit and or regulate electric power feeding state from the generation unit to an electric power feeding destination, and a controller (30) to control the state switch based on the output from the power generation state detector.    USE - Tidal current and ocean current electric power generation system.    ADVANTAGE - Electric power can be efficiently obtained using flow of seawater. Output state and or electric power feeding state of the electric power generation unit can be optimized correctly at time of change of tidal current or ocean current by being based on the detected seawater flow as well as data of estimated tide level. System maintenance can be performed safely and efficiently by stopping output or electric power feeding from the generation unit. Setting a mains power supply as an electric power feeding destination ensures efficient reverse power flow to the same power supply. More efficient and stable system use is possible by stopping electric power feeding when generated electric power output is low. Using an electrical storage device as the electric power feeding destination ensures efficient, lower cost transport of electric power without encountering power transmission losses usually associated with power transmission cables.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a power transmission method.    DESCRIPTION OF DRAWING(S) - The drawing shows the block diagram of a tidal current and ocean current electric power generation system. (Drawing includes non-English language text).    Tidal current and ocean current electric power generation system (1)    Electric power generation unit (10)    Controller (30)    Electric power generation state detector (40)    State switch (50)