Abstract: A rotary piston compressor with inlet and outlet passages the confinements of which for the inlet and outlet of the medium to be conveyed to the working chambers have controlling functions in cooperation with sealing elements. When the piston is within the region from the dead point of the piston to a point as far as to a location of the piston being turned further by a few degrees measured relative to turning of the eccentric shaft the leading seal element in the direction of piston rotation is located immediately preceeding the start of the inlet passage which communicates with a space of relatively low pressure.