To provide a fail-safe mechanism of a motor-driven hydraulic pressure generator capable of surely generating hydraulic pressure even when failure is caused in an electric system.

This fail-safe mechanism of the motor-driven hydraulic pressure generator has a pump part capable of generating the hydraulic pressure by being electrically operated, an actuator operated by the hydraulic pressure generated by the pump part, an accumulator oil chamber 18 communicating with the actuator via a first directional control valve 21, and capable of accumulating the hydraulic pressure generated in the pump part, and an air pressure source 25 capable of supplying air pressure to a back pressure chamber 19 of the accumulator oil chamber via a second directional control valve 23, and is characterized by supplying the hydraulic pressure of the accumulator oil chamber 18 to the actuator by the air pressure from the air pressure source.