To provide a compression type refrigerating machine and its capacity control method capable of stably controlling a capacity to lower load without bringing surging and extreme efficiency degradation.

This compression type refrigerating machine comprises an evaporator 10, a multistage compressor 13, a condenser 15, an economizer 17 and an expanding mechanism 19. A control valve 33 for opening and closing steam piping 31 is disposed in the steam piping 31 communicating the economizer 17 and an intermediate section of a plurality of compression stages 13a, 13b of the multistage compressor 13. Refrigerating effect is reduced by closing the control valve 33 and eliminating intermediate cooling effect by the economizer 17.