A cartridge device has a recording and reproducing unit for recording an information signal on and/or reproducing an information signal from a recording medium of a recording medium cartridge, the case having a positioning hole. A chassis of the device has a base and a projection projecting from the base toward a holder for being inserted in the positioning hole. An ejection slider is slidably supported on the chassis for sliding movement selectively in a first sliding direction to move the holder from the first to second position and a second sliding direction, which is opposite to the first sliding direction, to move the holder from the second to first position. The projection has a recess defined therein. The ejection slider has a portion insertable into the recess when the election slider is moved in the first sliding direction.