A variable-capacity gas compressor comprising a cylinder front and rear side blocks attached to both ends of the cylinder, a control plate formed with a recess or suction port which communicates with a communication port in the front side block and thereby forms a path for gas to flow into a cylinder chamber. The control plate is secured to the inner side of the front side block so that it may rotate within a given angular range. A driving means for driving the control plate and a control mechanism for controlling the driving means are provided so that the gas comnpressor is able to increase the cooling efficiency in the passenger compartment of an automobile in the beginning period of operation and to subsequently prevent any excessive cooling during continuous operation.