A recording medium storage cassette comprising: a cassette base for storing recording media; a recording medium loading plate disposed in the cassette base in a swingable manner so that its part on a downstream side in a recording medium conveying direction can move up and down about an axis in its part on an upstream side in the recording medium conveying direction; a rack formed on a bottom surface portion of the cassette base so as to extend along the recording medium conveying direction; and a rear end cursor which can move along the rack and aligns rear end positions of the recording media, characterized in that the rear end cursor includes a cursor main body portion, an abutting portion which can move along the recording medium conveying direction with respect to the cursor main body portion so as to abut rear ends of the recording media, a lock portion disposed upstream side of the abutting portion in the recording medium conveying direction so as to face the abutting portion and having a protrusion for engaging with the rack, and a biasing member disposed between the abutting portion and the lock portion so as to bias the abutting portion and the lock portion in a direction away from each other, and the engagement between the protrusion of the lock portion and the rack is locked when the lock portion is biased toward the upstream side in the recording medium conveying direction, while the engagement is released when the lock portion is swung toward the downstream side in the recording medium conveying direction with respect to the cursor main body portion against the biasing force of the biasing member. a cassette base for storing recording media; a recording medium loading plate disposed in the cassette base in a swingable manner so that its part on a downstream side in a recording medium conveying direction can move up and down about an axis in its part on an upstream side in the recording medium conveying direction; a rack formed on a bottom surface portion of the cassette base so as to extend along the recording medium conveying direction; and a rear end cursor which can move along the rack and aligns rear end positions of the recording media, characterized in that the rear end cursor includes a cursor main body portion, an abutting portion which can move along the recording medium conveying direction with respect to the cursor main body portion so as to abut rear ends of the recording media, a lock portion disposed upstream side of the abutting portion in the recording medium conveying direction so as to face the abutting portion and having a protrusion for engaging with the rack, and a biasing member disposed between the abutting portion and the lock portion so as to bias the abutting portion and the lock portion in a direction away from each other, and the engagement between the protrusion of the lock portion and the rack is locked when the lock portion is biased toward the upstream side in the recording medium conveying direction, while the engagement is released when the lock portion is swung toward the downstream side in the recording medium conveying direction with respect to the cursor main body portion against the biasing force of the biasing member.