There are provided with a determination means for determining whether or not the correlation between the pressure value detected by the primary pressure sensor and the pressure value detected by the secondary pressure sensor is an actually impossible relation (Step 5), and a switchover means for switching over to an open control while prohibiting a feedback control when the correlation is determined to have become a relation actually impossible by the determination means (Step 6). Presence or absence of a fault to the primary pressure sensor or the secondary pressure sensor (particularly, fault of fixed output voltage) is judged based on the correlation between the output voltage of the primary pressure sensor and the output voltage of the secondary pressure sensor to prohibit the control of a primary pressure and a secondary pressure using the hydraulic pressure sensors when it is judged that there is a fault.