A magnetic recording/reproducing apparatus includes a head for performing recording/reproducing, a chassis for positioning the head, a cassette holder for positioning a cassette on the chassis, the cassette including an opening portion through which a recording medium is received or drawn out, a cassette holder supporting member for supporting the cassette holder on the chassis, and a casing which contains these component parts. The cassette holder supporting member has a substantially U-shape, facing three side surfaces of the cassette except the opening portion, and includes integrally formed fastening portions to be secured on the casing. The cassette holder supporting member is fastened to the casing through two fastening portions, and the chassis is directly fastened to the casing in one portion of the chassis.