A hand mechanism of an accessor, capable of gripping a recording medium cartridge in a horizontal condition thereof. The accessor automatically exchanges the recording medium cartridge between a cell unit having a plurality of cells each accommodating the recording medium cartridge and a recording medium drive unit for performing read/write of data from/to the recording medium cartridge. The hand mechanism includes a base mounted swingably about a vertical axis, a grip hand mounted on the base movably between an advanced position and a retracted position, for gripping the cartridge, and a tray mounted on the base and under the grip hand movably between an advanced position projecting from the base and a retracted position. The hand mechanism further includes a cartridge gripped condition correcting mechanism for correcting a gripped condition of the cartridge gripped by the grip hand.