PURPOSE: To securely position a cassette holder by engaging an engagement part with a lock part and positioning the cassette holder in the cassette loader device when the cassette holder is drawn out to in front of the front surface of a magnetic recording and reproducing device main body.

CONSTITUTION: The cassette holder 10 which is drawn out to in front of the front surface of the magnetic recording and reproducing device main body 1 to load or unload a tape cassette C forms part of a tray 20. The tray 20 is formed in a frame shape by providing a front plate between a right and a left side plate extending in a front and a rear direction, hooks are fixed on the external surfaces of the side plates, and a positioning hole 24 as the engagement part is formed in the front plate. Then the tray 20 engages a projection 25 as the lock part formed inside the front surface of an arm part 100a at a front projection position and is positioned. Consequently, the cassette holder 10 is securely and easily positioned in the cassette loader device.