PURPOSE: To precisely detect pressure in an operational chamber, by forming a hole communicated with an end of a main shaft on a discharge side at a tooth groove of a rotor, providing a pressure sensor at an opening portion of the hole, and transmitting a pressure signal from a signal generator means at the end of the main shaft.

CONSTITUTION: There is formed a hole 11 communicated with an end of a main shaft 10 on a discharge side at a tooth groove of a rotor 7 of a screw compressor. A pressure sensor 12 is provided at an opening portion of the hole 11. A pressure signal generator means 17 utilizing a FM signal is provided at the end of the main shaft, and is connected with the pressure sensor 12 through a cable 16 in the hole 11. A pressure signal receiver means 19 is provided in a screw compressor body 1 to transmit a received signal to an external equipment.