An inventive recording medium loader includes a connector provided on a chassis for engagement with a front edge of a generally rectangular planar recording medium, and a tray provided on the chassis for transporting the recording medium toward and away from the connector. An engagement piece having a claw to be brought into and out of engagement with a notch formed in the recording medium is provided on the tray, and a cam is provided in an engagement piece movement path on the chassis. Before the forward edge of the recording medium is engaged with the connector, the claw is brought into engagement with the notch of the recording medium by the cam to lock the recording medium on the tray. In this state, the recording medium is brought into engagement with the connector.