To absorb an excessive load even if it acts on the front part of a grinder body by making the rear part of the grinder body vertically rockable to an attachment, and energizing it downward.

A pair of guide shafts are electedly installed on a rear holder 516. A cylindrical stopper 521 is mounted on the upper end, and a coil spring 520 is compressed and installed between the stopper 521 and an attachment to energize the rear holder 516 and, thus, the rear part of a grinder body 510 upward. A lock lever 526 is inserted into a bracket fixed to the upper front part of the attachment, whereby a stopper 523 can be locked in downward rocked state. In grinding, the lock lever 526 of the grinder is pulled to lay the stopper 523 in upward rocked state, so that the grinder 511 body can be rocked. According to this, an excessive load acting on the grinder can be absorbed.