A housing includes a crank chamber and cylinder bores. Pistons are accommodated in the cylinder bores. A drive shaft is supported by the housing to pass through the crank chamber. A lug plate is fixed to the drive shaft. The pistons are coupled to the lug plate, which converts rotation of the drive shaft into reciprocation of the pistons and compresses gas in the cylinder bores. A thrust bearing is located between the housing and the lug plate and transmits a thrust load applied to the lug plate. The thrust bearing includes a front race located next to the housing, a rear race located next to the lug plate, and rollers located between the front and rear races. A front seat for supporting the front race is formed on the housing. A rear seat for supporting the rear race is formed on the lug plate. The diameters of the front and rear seats are different, which causes elastic deformation of the races when a thrust load is applied.