A printing medium feeding cassette for accommodating printing media for use in an image forming apparatus, comprising: a cassette body having arranged therein a body hook formed along an adjustment direction, the adjustment direction being one of a width direction and a length direction of the printing media; a knock-up plate supported in the cassette body, the knock-up plate having a surface for supporting thereon the printing media; and an aligning unit supported on the cassette body for aligning the printing media loaded on the knock-up plate, the aligning unit having a unit body movable along the adjustment direction, a unit hook configured to selectively come into an engaging contact with the body hook and a hook releaser coupled to the unit body, characterised in that: when a push force is applied in a first adjustment direction to the hook releaser to move the aligning unit in the first adjustment direction, the hook releaser rotates about a hinge shaft and moves the unit hook upward with respect to and towards the hinge shaft by the rotation of the hook releaser, causing the unit hook to be released from the body hook, and when a pull force is applied in a second adjustment direction which is opposite to the first adjustment direction to the hook releaser to move the aligning unit in the second adjustment direction, the hook releaser rotates about the hinge shaft and moves the unit hook upward with respect to and towards the hinge shaft by the rotation of the hook releaser causing the unit hook to be released from the body hook. a cassette body having arranged therein a body hook formed along an adjustment direction, the adjustment direction being one of a width direction and a length direction of the printing media; a knock-up plate supported in the cassette body, the knock-up plate having a surface for supporting thereon the printing media; and an aligning unit supported on the cassette body for aligning the printing media loaded on the knock-up plate, the aligning unit having a unit body movable along the adjustment direction, a unit hook configured to selectively come into an engaging contact with the body hook and a hook releaser coupled to the unit body, characterised in that: when a push force is applied in a first adjustment direction to the hook releaser to move the aligning unit in the first adjustment direction, the hook releaser rotates about a hinge shaft and moves the unit hook upward with respect to and towards the hinge shaft by the rotation of the hook releaser, causing the unit hook to be released from the body hook, and when a pull force is applied in a second adjustment direction which is opposite to the first adjustment direction to the hook releaser to move the aligning unit in the second adjustment direction, the hook releaser rotates about the hinge shaft and moves the unit hook upward with respect to and towards the hinge shaft by the rotation of the hook releaser causing the unit hook to be released from the body hook. when a push force is applied in a first adjustment direction to the hook releaser to move the aligning unit in the first adjustment direction, the hook releaser rotates about a hinge shaft and moves the unit hook upward with respect to and towards the hinge shaft by the rotation of the hook releaser, causing the unit hook to be released from the body hook, and when a pull force is applied in a second adjustment direction which is opposite to the first adjustment direction to the hook releaser to move the aligning unit in the second adjustment direction, the hook releaser rotates about the hinge shaft and moves the unit hook upward with respect to and towards the hinge shaft by the rotation of the hook releaser causing the unit hook to be released from the body hook.