Disclosed is a vacuum preventing device of a scroll compressor comprising: a discharge cover installed at a body of a fixed scroll for dividing inside of a case into a discharge region and a suction region; a vacuum cylinder installed in the discharge cover thus to be connected to a compression chamber formed between the fixed scroll and an orbiting scroll and having a pressure space therein so that the discharge region can be connected to the suction region; a piston movably installed in the pressure space for selectively connecting the discharge region with the suction region by a pressure difference between the compression chamber and the suction region; and an elastic member installed in the pressure space for providing an elastic force to the piston.