PROBLEM TO BE SOLVED: To provide an inexpensive and compact structure. A one-way power transmission device (1) for a working machine according to the present invention is provided with a rotary shaft (2) having a spline (2a) and a gear hole (3b) meshing with the spline (2a) of the rotary shaft (2) provided on the inner circumference. 3a, which is slidable with respect to the rotary shaft 2 and configured to be relatively non-rotatable, and a second motion transmission element 3 configured to be relatively rotatable with respect to the rotary shaft 2. The element 4 and the urging means 5 for urging the first transmission element 3 and the second transmission element 4 to contact each other are provided, and between the rotary shaft 2 and the second transmission element 4. The female screw 3c and the male screw 4b, which are screwed to each other when a power in a relatively regular rotation direction is input and are screwed out when a power in a reverse rotation direction is input, are the first transmission element 3 and the first transmission element 3. It is provided relatively to the second transmission element 4. [Selection diagram]
