A scroll compressor having a vacuum preventing structure includes: a casing forming a receiving space therein; a fixed scroll fixed to a main frame installed in the casing, and including a back pressure passage at an outer side surface thereof, a discharge pressure hole formed at one side of the back pressure passage such that the back pressure passage and a discharge pressure space of the casing can communicate with each other, a middle pressure hole formed at another side of the back pressure passage such that the back pressure passage and a compression space of the casing can communicate with each other, and a suction pressure hole formed at still another side of the back pressure passage such that the back pressure passage and a suction pressure space can communicate with each other; an orbiting scroll positioned between the fixed scroll and the main frame and forming a compression space by being coupled with the fixed scroll; a piston slidably installed in the back pressure passage, for opening or closing the discharge pressure hole; an elastic member installed in the back pressure passage, for supporting the piston; and a stopper for closing an inlet of the back pressure passage.