PURPOSE: To generate always an optimum DC for control even in case of variable speed reproducing by changing the period of a generated saw tooth wave signal in accordance with a tape speed.

CONSTITUTION: When a rotation pulse signal FG corresponding to the running speed of a magnetic tape is generated, a saw tooth wave generating circuit 1 outputs a saw tooth wave signal AC' where a two-field time is one period. Meanwhile, the signal FG is shifted successively by an n/2-stage shift register 5 and is supplied to an n-notation counter 6. Consequently, a saw tooth wave generating circuit 4 outputs a saw tooth wave signal BC' whose phase is shifted from that of the signal AC' by 180°. A head switching signal HS is differentiated, and a positive-polarity differential signal corresponding to the rise of this signal HS is outputted from a diode 10, and the signal AC' is sampled and held by turning-on of a transistor TR15. Consequently, an inverting amplifier 21 generates a controlling DC signal ADC for a head A. By an inverted signal of the signal HS which is supplied through an inverter 11, a controlling DC signal BDC for a head B is generated synchronously with the fall of the signal HS. The similar operation is performed also in case of variable speed reproducing.