A recording medium storage apparatus has a storage cassette and a lock mechanism. The lock mechanism restricts movement of the storage cassette in the drawing direction. The lock mechanism has an engaging portion on an apparatus body and an engaged portion on the storage cassette. While the storage cassette is drawn out of the apparatus body, an abutting portion of the engaging portion moves along a first slope on the engaged portion toward a peak portion while swinging in a second direction in which it retracts from the engaged portion, and meanwhile the engaged portion rotates in a third direction so that the peak portion is displaced from a protruding position to a guiding position.