A magnetic disc unit into and from which a disc case housing a magnetic disc is loaded and ejected includes a chassis, a magnetic head, a slide member being capable of sliding between a first position and a second position, a latch member fixing said slide member at the first position when the disc case is ejected, being pushed by the disc case inserted in said magnetic disc unit at a time of inserting the disc case and fixing said slide member at the second position when the disc case is loaded into said magnetic disc unit and is positioned at a predetermined set position, an arm member rotated by a sliding operation of said slide member, a clamping member clamping the magnetic disc housed in the disc case and a connection mechanism making said clamping member clamp the magnetic disc when said arm member is positioned at a second rotation position and separating said clamping member from the magnetic disc when said arm member is positioned at a first rotation position.