PURPOSE: To finely adjust the tension of a tape and to provide the precision contact of the tape and a drum by generating the change of the biasing force of a coil spring added to a tension arm corresponding to the rotation of an adjustment knob.

CONSTITUTION: This tension adjustment device 40 of the tape is provided between a supply reel base 30 and a head drum 32 so as to adjust the tension of a magnetic tape T and the device 40 is provided with a tension pole 50. Also, to a deck 34, a knob 62 suitable for operating a slider 56 in a horizontal direction along a guiding oblong hole 54 is freely rotatably mounted. The slider 56 is slid along the oblong hole 54 by the rotation of the knob 62 and the energizing force of the coil spring 52 added to the tension arm 42 is adjusted.