A chain saw is provided with an adjustment mechanism that adjusts the tension of a saw chain 4 attached along a guide bar 3 projecting from a main body 2. The adjustment mechanism has a rotation shaft 55 that is provided with a feed screw, a moving element 70 that is moved on the rotation shaft 55 in an axial direction along with rotation of the rotation shaft 55 and moves the guide bar 3 forward/backward with respect to the main body 2, and a transmission mechanism including an internal gear 51 provided on an inner peripheral surface of an adjustment dial 50 rotatably provided on the main body 2 and an external gear 52 disposed on an inner side of the adjustment dial 50 and engaged with the internal gear 51. When the internal gear 51 is rotated along with rotation of the adjustment dial 50, the rotation shaft 55 is rotated via the external gear 52.