Screw compressor and refrigeration apparatus

A screw compressor comprising:

• a screw rotor;
• a plurality of gate rotors having gates that mesh with the screw rotor;
• a casing into which the screw rotor is rotatably inserted, the casing having a cylindrical wall through which the gates penetrate;
• and
• an adjustment mechanism configured to adjust a pressure of a fluid in the casing,
• a plurality of compression chambers being formed inside the cylindrical wall by the screw rotor and the gates,
• the plurality of compression chambers include
• a first compression chamber in which the fluid introduced into the casing with a suction pressure is compressed to a pressure higher than the suction pressure, and
• a second compression chamber to which the fluid compressed in the first compression chamber is sent via an intermediate pressure space, and
• the adjustment mechanism being configured to adjust an intermediate pressure, which is a pressure of the fluid in the intermediate pressure space, in a two-stage operation in which the fluid is compressed in the first compression chamber and the second compression chamber.