A slant plate type compressor (10) with a capacity or displacement adjusting mechanism (400) is disclosed. The compressor (10) includes a housing (20) having a cylinder block (21) provided with a plurality of cylinders (70) and a crank chamber (22). A piston (71) is slidably fitted within each of the cylinders (70) and is reciprocated by a drive mechanism which includes a slant plate (50) having a surface with an adjustable incline angle. The incline angle is controlled according to the pressure in the crank chamber. The pressure in the crank chamber (22) is controlled by a control mechanism (400) which comprises a first passageway (150) linking the crank chamber (22) and the suction chamber (241) and a valve device (19) which controls the closing and opening of the first passageway (150). The valve device (19) includes a valve element which directly controls the closing and opening of the first passageway (150), a first valve control device (19) which controls the position of the valve element in response to pressure in the crank chamber (22), and a second valve control device (400) which include a second passageway (905,903,901) linking the crank chamber and the discharge chamber and an actuator (195) disposed in the second passageway. The second valve control device (400) controls the predetermined crank pressure operating point of the first valve control device (19). The operation of the second valve control device (400) is controlled in response to changes in the thermodynamic characteristics of the refrigerant circuit so as to open and close the second passageway (903,901).