A coolant compressor (1), comprising a piston-cylinder unit (2) that compresses a coolant, said piston-cylinder unit comprising a cylinder housing (4) and a piston (3) held in a piston bore (5) of the cylinder housing (4), wherein the cylinder housing (4) is sealed in an axial direction by a valve plate (6) and a cylinder cover (7). In order to facilitate the simple and flexible mounting of the valve plate (6) at the cylinder housing (4), it is provided according to the invention that the valve plate (6) is countersunk in its operating position in the piston bore (5) of the cylinder housing (4) and is fastened at the cylinder housing (4) or in the piston bore (5) by way of a material bond connection.