To provide a hydraulic pressure control device of a fluid transmission device capable of transmitting power from a power source to a pump impeller even when a problem occurs in a hydraulic circuit in a composition having an impeller clutch.

A turbine runner 14 is rotated by receiving oil from the pump impeller 12. The hydraulic pressure control device of the fluid transmission device comprises a lock-up clutch 15a capable of directly connecting the turbine runner 14 to an engine output shaft 1, and the impeller clutch 13a capable of disconnecting the pump impeller 12 from the engine output shaft 1. The hydraulic pressure control device is equipped with a switching valve 29 arranged at an oil passage between the impeller clutch 13a and a control valve 31a for the impeller clutch and connecting the control valve 31a for the impeller clutch or a control valve 33a for the lock-up clutch to the impeller clutch 13a to be able to switch between these valves 31a, 33a.