In a piston type compressor, a housing includes a cylinder head which defines a discharge chamber and a cooling chamber. The cooling chamber located adjacent to the discharge chamber surrounds the discharge chamber. The housing also defines a suction chamber, a compression chamber, and a crank chamber. The cooling chamber is isolated from the suction chamber. Gas is introduced from outside of the housing into the suction chamber. A rotary shaft is rotatably supported in the housing. The cam is accommodated in the crank chamber. A piston is operatively coupled to the rotary shaft through the cam. Rotation of the rotary shaft is converted to reciprocation of the piston. A seal member shuts communication between the cooling chamber and an atmosphere outside the compressor to seal an inside of the cylinder head. An introducing passage interconnects the cooling chamber and the crank chamber.