A compressor including a motor, a piston reciprocating by the motor, a crankcase having a middle wall portion formed with a communication hole, the crankcase housing the piston, a cylinder body secured to an inner surface of the middle wall portion, the cylinder body and the wall portion defining a cylinder chamber, and reciprocation of the piston increasing or decreasing a capacity of the cylinder chamber, and a cylinder head secured to an outer surface of the middle wall portion, the cylinder head and the middle wall portion defining an exhaust chamber communicated with the cylinder chamber through the communication hole.