PURPOSE: To alleviate contact of a magnetic tape with a delay side window part edge and to reduce damage to the tape by positioning one end in the delay side edge of a window part of a rotary drum and positioning its one part in a groove outside a contact range of the rotary drum with the tape, i.e., a circumferential groove provided in the window part edge.

CONSTITUTION: The circumferential groove 15 is provided on an outer circumference of the rotary drum 13, passing the delay side window part edge 57 and having the same height as a magnetic head. Thus, air is entered into between the magnetic tape and the delay side window part edge from the groove on the rotary drum, so that the tape is prevented from sticking to the delay side window part edge, and abrasion of the drum and damage to the tape are reduced. Moreover, magnetic dust on the tape is scraped out and clogging of the head is reduced. In addition, the magnetic dust stuck on the tape is efficiently scraped out into the groove, and hence the clogging is further reduced.