There is provided a thin optical disk device having a slot-in mechanism which is able to smoothly carry out operations of clamping and releasing an optical disk, including an optical pickup which carries out reading and/or writing from/to the optical disk, a turntable which places the optical disk at an operating position of the optical pickup and rotates the optical disk, a clamper which is arranged at an approximate center of the turntable and can freely advance and retreat in a direction of a diameter of the optical disk, and a device for clamping an inside diameter section of the optical disk at a location directly above the clamper with the optical disk being held by sandwiching the optical disk and for pressing the inside diameter section from the side of a non-writing surface of the optical disk and clamping the inside diameter section to the clamper.