Provided are a guide pin configured to support a corner of a photo mask using a double slide structure, a photo mask supporting unit including the same, and a photo mask cleaning apparatus including the same. The photo mask supporting unit includes a supporting plate, a supporting shaft which supports the supporting plate from under the supporting plate, a supporting plate driver configured to rotate the supporting plate, and a guide pin provided as a plurality of guide pins on the supporting plate to support a photo mask and including at least one column protruding upward from a flat surface and having a first sliding portion and a second sliding portion formed on a side surface of the column to be inclined downward to have different angles.