NOVELTY - The apparatus has hydraulic transmission unit (10) comprising hydraulic pump (12) driven by rotating shaft (8) and hydraulic motor (14) driven by pressurized oil supplied from hydraulic pump. Synchronous generator (20) generates power and couples with grid (50) without intervening frequency conversion circuit. Transmission controller (40) controls hydraulic transmission in normal operation mode to adjust displacement of hydraulic pump and hydraulic motor. Rotating shaft rotates at rotational speed varied with respect to flow speed of renewable energy.    USE - Renewable energy type power generating apparatus such as wind turbine generator for generating power from renewable energy such as wind, tidal current, ocean current and river current. Can also be used in tidal generator, ocean current generator and river current generator.    ADVANTAGE - Since transmission controller controls hydraulic transmission in normal operation mode to adjust displacement of hydraulic pump and hydraulic motor, rotating shaft can rotate at rotational speed varied with respect to flow speed of renewable energy. Since power system stabilizer suppresses generator swing promptly by controlling the exciter to increase damping torque, steady-state stability of synchronous generator is improved. Since the field current is increased immediately after terminal voltage of synchronous generator decreases due to fault event at grid, the induced voltage inside generator and electrical output power of generator are increased.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for generating power using renewable energy in renewable energy type power generating apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of hydraulic transmission unit and transmission controller of wind turbine generator.    Rotating shaft (8)    Hydraulic transmission unit (10)    Hydraulic pump (12)    Hydraulic motor (14)    Synchronous generator (20)    Transmission controller (40)    Grid (50)