A vacuum preventing device of a scroll compressor includes: a chamber formed at one side of a fixed scroll and having a suction pressure hole, a middle pressure hole and a discharge pressure hole communicating with a suction pressure zone, a middle pressure zone and a discharge pressure zone, each formed at a certain portion of an inner circumferential surface; an open and shut member installed inside the chamber and selectively communicating the discharge pressure hole and the suction pressure hole by virtue of a gas pressure of the middle pressure zone and an elastic force of a spring; and a gas leakage preventing unit for preventing a gas leakage in a normal operation by reducing a clearance between an inner wall of the chamber positioned at the side of the discharge pressure hole and the open and shut member.