A multi-stage compressor is disclosed, which comprises: two motion converters driven by one driving shaft and converting a rotary motion to a straight-line reciprocating motion; first and second pistons (62) connected to one of the motion converters in opposite directions and moving reciprocatively in a straight line; and third and fourth pistons (72) connected to the other one of the motion converters in opposite directions, arranged at a predetermined angle with respect to the first and second pistons (62), and moving reciprocatively in a straight line, and which is characterized in that at least two of the four pistons operate for first-stage compression and at least one of the others operate for second-stage compression.