NOVELTY - Each selector valve (56,57) has first, second, third and fourth ports to which a pressurized water supply line (12), supply and removal water pipe path (50A-50D), drain pipe path (54) and supply and removal water pipe path (54A-54D) are respectively connected. The valve body operates such that the first and third ports are separately connectable to the second and fourth ports.    USE - Hydraulic electric power generation system.    ADVANTAGE - Transforms pressure of pressurized water efficiently into driving force that is transmitted to generator, thereby improving electric power generation efficiency.    DETAILED DESCRIPTION - A piston cylinder mechanism (24) includes pistons (34A-34D) that reciprocatingly move inside cylinders (32A-32D) due to pressurized water supplied from the pressurized water supply line, thereby driving a generator (16). A pressurized water distribution unit (28) automatically switches the distribution of the pressurized water into the cylinders by the partial rotational drive force from the piston cylinder mechanism. The pressurized water distribution unit includes the supply and removal water pipe paths (50A-50D) each connected to a chamber of the corresponding cylinder, and the supply and removal water pipe paths (52A-52D) each connected to another chamber of the corresponding cylinder. The drain pipe path drains the water ejected from the cylinders to the external. A valve drive unit switches the selector valves based on the movement of the pistons. The selector valves connect any of the supply and removal water pipe paths to the pressurized water supply line and drain pipe path.    DESCRIPTION OF DRAWING(S) - The figure is a longitudinal cross-sectional view of the hydraulic electric power generation system.    Pressurized water supply line (12)    Generator (16)    Piston cylinder mechanism (24)    Pressurized water distribution unit (28)    Cylinders (32A-32D)    Pistons (34A-34D)    Supply and removal water pipe path (50A-50D,54A-54D)    Drain pipe path (54)    Selector valve (56,57)