To improve quality and also to prolong the service life of a gear driving part by switching the setting of a backlash in the gear driving part according to a cutting mode or transfer mode in a thermal cutting device having the gear driving part, thereby stabilizing a cutting part.

In this thermal cutting device, having a gear driving part 2, the operation based on the cutting mode by which a work W is cut and the operation based on the transfer mode by which a working head 6 is transferred up to the prescribed working point on the work W are respectively executed by a carriage 1 transferable in the back and forth directions and the working head 6 transferable in the left and right direction on the carriage 1. A backlash in the gear driving part 2 is set small in cutting mode, while the backlash in the gear driving part 2 is set properly transfer mode.