PURPOSE: To prevent the parallelism of drive shaft and driven shaft to each other from disorder with a simple structure by allowing high temperature of discharged compressed air to act at least between the drive shaft end and driven shaft end of a housing at the opposite side to one end side of the drive shaft provided with a drive gear.

CONSTITUTION: In a mechanical compressor having a drive shaft and driven shaft provided respectively with rotors 2, 3, the drive shaft 4 is on one end side with a drive gear 6 and on the outer surface of a housing 1b at the other end side of the drive shaft 4 with an air chamber 14 including a space between the respective extensions of at least the drive shaft and driven shaft and characteristically communicating to a discharge port of the mechanical compressor.