To provide a power transmission device for a work machine provided with a torque limiter of easy assembling.

A wheel of a worm reduction gear is comprised of two parts of a boss part 27 and a gear part 26. The gear part 26 is pressed in the boss part 27. The boss part 26 and the gear part 27, therefore, rotate as one body as far as a normal torque is transmitted and the gear part 26 freely rotates relatively against the boss part 27 in an excessive load condition. Or, a torque limiter is constructed at a location where the gear part 26 freely rotates relatively against the boss part 27. Sulfurizing treatment is applied on a contact surface 38 of the boss part 27 and a contact surface 39 of the gear part 27 constructing the torque limiter. The boss part 26 can be easily attached to an auger shaft by spline or the like. An auger transmission, therefore, is easily assembled even through the torque limiter is built in. The life of the torque limiter can be extended by applying sulfurizing treatment.