Provided is a hydraulic pressure control device. A hydraulic pressure control device supplies hydraulic pressure to a piston using solenoid valves and performs 2:1 switching processing of stopping the supply of hydraulic pressure to the piston using a solenoid valve when the piston is switched to a parking locked state. When the piston is not switched to a side that is to be a parking locked state, hydraulic pressure is supplied to two solenoid valves, and 2:0 switching processing of stopping the supply of hydraulic pressure to the piston by solenoid valves is performed. Then, a reporting processing of reporting that at least one of the solenoid valves has failed is performed.