Compressor (1) having a region of pressure intermediate between discharge pressure and suction pressure (especially, crank chamber (10)), characterized in that a valve mechanism (21) is provided for introducing discharge gas into the region of intermediate pressure so as to render constant the difference between intermediate pressure and suction pressure. A compressor structure is provided which can stably introduce a mixture of discharge gas and refrigerating machine oil into the crank chamber without using pressure reducing means such as an aperture and in a manner easy to form a passageway, thereby improving the lubricity of rolling part and slide part in the crank chamber.