PURPOSE: To read pressure over a wide range by expanding the measuring function of a pressure sensor by operating a three-way solenoid valve to change over a connection state to a suction manifold and the pressure sensor or the pressure sensor and an one-way valve.

CONSTITUTION: A pressure sensor 12 is connected to a suction manifold 2 through a pressure passage 10 and a three-way solenoid valve 14 is provided on the way of the passage 10 and the manifold 2 is connected to the first communication port part 14-1 of the valve 14. The sensor 12, the valve 14 and other sensors or a device to be driven are connected to a control part 18. The valve 14 is operated when a predetermined execution condition is formed to connect the sensor 12 to an one-way valve 16 and, when the reading operation of atmospheric pressure is completed, the valve 14 is subjected to OFF-operation to change over a connection state in order to connect the manifold 2 to the sensor 12 to detect atmospheric pressure.