A refrigerator comprising: a cabinet comprising a storage compartment having an open front side; a sliding shelf provided on a rear wall of the storage compartment so as to be dischargeable forward; a folding shelf (300, 500) disposed at a first position, at which the folding shelf (300, 500) is disposed in a horizontal direction of the storage compartment to form a single plane together with the sliding shelf, or disposed at a second position, at which the folding shelf (300, 500) is rotated from the first position to be disposed in a vertical direction of the storage compartment; a hinge unit configured to rotatably couple the folding shelf (300, 500) to a side surface of the storage compartment; a rotation resistor provided on the side surface of the storage compartment to resist rotation of the folding shelf (300, 500); and a sagging preventer comprising a protrusion provided on a bottom surface of the folding shelf (300, 500) and a press portion provided on the hinge unit to selectively press the protrusion, in order to prevent sagging of the folding shelf (300, 500) disposed at the first position, wherein the rotation resistor comprises: a fixing body fixed to the side surface of the storage compartment; characterized in that the rotation resistor comprises a protruding arm configured to protrude from the fixing body and comprising a plurality of holding grooves indented in a distal end thereof and a stepped portion formed between the holding grooves; and a holder configured to be elastically pressed by the folding shelf (300, 500) and selectively accommodated in one of the holding grooves. a cabinet comprising a storage compartment having an open front side; a sliding shelf provided on a rear wall of the storage compartment so as to be dischargeable forward; a folding shelf (300, 500) disposed at a first position, at which the folding shelf (300, 500) is disposed in a horizontal direction of the storage compartment to form a single plane together with the sliding shelf, or disposed at a second position, at which the folding shelf (300, 500) is rotated from the first position to be disposed in a vertical direction of the storage compartment; a hinge unit configured to rotatably couple the folding shelf (300, 500) to a side surface of the storage compartment; a rotation resistor provided on the side surface of the storage compartment to resist rotation of the folding shelf (300, 500); and a sagging preventer comprising a protrusion provided on a bottom surface of the folding shelf (300, 500) and a press portion provided on the hinge unit to selectively press the protrusion, in order to prevent sagging of the folding shelf (300, 500) disposed at the first position, wherein the rotation resistor comprises: a fixing body fixed to the side surface of the storage compartment; characterized in that the rotation resistor comprises a protruding arm configured to protrude from the fixing body and comprising a plurality of holding grooves indented in a distal end thereof and a stepped portion formed between the holding grooves; and a holder configured to be elastically pressed by the folding shelf (300, 500) and selectively accommodated in one of the holding grooves.