PURPOSE: To permit an electronic means to detect that a magnetic tape has been loaded on a machine reel by monitoring the terminal voltage of the reel motor in order to detect whether a tension is applied to the magnetic tape or not.

CONSTITUTION: Until a magnetic tape is loaded on a machine reel a transistor 10 is turned ON or OFF according to the output 1 or 0 from an AND circuit 18, so that a file motor 11 repeats revolution and stop. The terminal voltage of a capacitor 14 increases when the motor 11 rotates, and decreases when the motor 11 stops. A comparison circuit 15 outputs -V0 when the input voltage is Vref (reference voltage)+V0, and +V0 when the input voltage is Vref-V0, and so the circuit 18 outputs a 1. When the magnetic tape is loaded on the machine reel, the motor 11 receiving tension through the magnetic tape increases the number of revolution. Consequently, the terminal voltage of the capacitor 14 no longer agrees with Vref- V0, and so the circuit 18 no longer output 1. Detection thereof this permits the detection of the fact whether the magnetic tape has been loaded or not.