Servo writer

A servo writer which writes a servo signal on a tape, which is paid off from a pay-off reel provided at an upstream side of a write head and is wound on a winding reel provided at a downstream side of said write head, by said write head, the writer comprising:

• a pay-off side motor paying off the tape from the pay-off reel by rotating said pay-off reel;
• a winding side motor winding the tape on the winding reel by rotating said winding reel;
• a first capstan roller and second capstan roller which are provided at the upstream side and down stream side of said write head, respectively, and by rotating the capstan rollers, run the tape in a state pinched between respective pinch rollers and the capstan rollers;
• a first tension detecting means which is provided between said first capstan roller and said second capstan roller and detects running tape tension;
• and
• a capstan roller controlling unit controlling a rotation speed of said first capstan roller and said second capstan roller so that tension detected by said first tension detecting means becomes constant,
• wherein said capstan roller controlling unit has a low pass filter attenuating a high frequency component of a tension signal detected by said first tension detecting means.