A scroll compressor with an apparatus for preventing vacuum of a scroll compressor, comprising: a casing having a hermetic inner space divided into a suction chamber of a low pressure and a discharge chamber of a high pressure; a fixed scroll fixedly installed at the casing between the suction chamber of the casing and the discharge chamber thus to form a compression chamber that consecutively moves by being engaged with an orbiting scroll, having an outlet through which a refrigerant compressed in the compression chamber is discharged to the discharge chamber, and having a bypass hole through which the suction chamber of the casing is connected to the discharge chamber, and having a middle pressure channel communicating with a discharge space of the compression chamber; the scroll compressor being characterized in that the apparatus for preventing vacuum comprises a valve block fixedly installed on an upper surface of the fixed scroll that belongs to the discharge space, having a single valve hole (155a, 251a), wherein the middle pressure channel is connected to the single valve hole (155a, 251a), having a discharge pressure channel (155b, 251b) penetratingly formed so as to be communicated with the discharge space in the middle of the single valve hole, and having a connection channel (155c, 251c) penetratingly formed so as to selectively communicate the discharge pressure channel (155b, 251b) with the bypass hole; and a single valve member (152, 252) slidably disposed at the single valve hole (155a, 251a), for opening the discharge pressure channel (155b, 251b) thereby supplying a refrigerant of the discharge chamber to the suction chamber when a pressure of the compression chamber is lowered to a pressure less than a certain pressure, and for closing the discharge pressure channel (155b, 251b) and blocking communication of said discharge pressure channel (155b, 251b) with the connection channel (155c, 251c), thereby preventing the refrigerant of the discharge chamber from backflowing into the suction chamber as long as the compression chamber maintains a pressure of at least said certain pressurewherein the connection channel (155c, 251c) is formed partially at a bottom surface of the valve block (151, 251) and between a bottom surface of the valve block (151, 251) and the bypass hole. a casing having a hermetic inner space divided into a suction chamber of a low pressure and a discharge chamber of a high pressure; a fixed scroll fixedly installed at the casing between the suction chamber of the casing and the discharge chamber thus to form a compression chamber that consecutively moves by being engaged with an orbiting scroll, having an outlet through which a refrigerant compressed in the compression chamber is discharged to the discharge chamber, and having a bypass hole through which the suction chamber of the casing is connected to the discharge chamber, and having a middle pressure channel communicating with a discharge space of the compression chamber; the scroll compressor being characterized in that the apparatus for preventing vacuum comprises a valve block fixedly installed on an upper surface of the fixed scroll that belongs to the discharge space, having a single valve hole (155a, 251a), wherein the middle pressure channel is connected to the single valve hole (155a, 251a), having a discharge pressure channel (155b, 251b) penetratingly formed so as to be communicated with the discharge space in the middle of the single valve hole, and having a connection channel (155c, 251c) penetratingly formed so as to selectively communicate the discharge pressure channel (155b, 251b) with the bypass hole; and a single valve member (152, 252) slidably disposed at the single valve hole (155a, 251a), for opening the discharge pressure channel (155b, 251b) thereby supplying a refrigerant of the discharge chamber to the suction chamber when a pressure of the compression chamber is lowered to a pressure less than a certain pressure, and for closing the discharge pressure channel (155b, 251b) and blocking communication of said discharge pressure channel (155b, 251b) with the connection channel (155c, 251c), thereby preventing the refrigerant of the discharge chamber from backflowing into the suction chamber as long as the compression chamber maintains a pressure of at least said certain pressurewherein the connection channel (155c, 251c) is formed partially at a bottom surface of the valve block (151, 251) and between a bottom surface of the valve block (151, 251) and the bypass hole.