PURPOSE: To obtain always the optimum recording current value, by using a detecting signal equivalent to the value of current or voltage supplied to a magnetic head circuit to control the gain of the current and voltage that is needed for the optimum recording current.

CONSTITUTION: It is possible to keep always the recording current of a video head 9 at the optimum recording current value in accordance with the secondary current of a rotary transformer 8 as long as the primary current and voltage of the transformer 8 can be varied along straight lines V3 and V4 respectively when the impedance Z of the head 8 varies from the designed standard value Z0 to ZL or ZH. In other words, the change is replaced and compensated for the impedance Z of the head 9 to its standard value Z0 in response to the current and voltage supplied to the primary side of the transformer 8 as long as the recording current is always kept at the optimum recording current value. In such a way, it is always possible to ensure the optimum recording current value despite a change of the impedance of the head 9.