PURPOSE: To enable the saw diameter to be recognized and thus improve the workability by detecting the existence of a circular saw in the diameter direction, that rotates in a dust collecting hood, and conducting an indication corresponding to the detecting output thereof.

CONSTITUTION: Switches such as a proximity switch or the like are arranged with separation in the direction of a diameter line corresponding to the retracting position of a circular saw 16. A detecting switch Sa outputs a detecting signal at the time of detecting the blade tip (b) of a maximum diameter of the circular saw 16. A detecting switch Sb outputs a detecting signal at the time of detecting the blade tip of an intermediate diameter of the circular saw and the base metal part (a) of the maximum diameter of the circular saw. The detecting switch Sc outputs a detecting signal at the time of detecting the blade (b) of a minimum diameter of the circular saw and the base metal parts (a) of the intermediate and maximum diameters of the circular saw. When these detecting switches Sa-Sc detect the circular saw and close the contact points, circuits l1, l2, l3, close respectively in accordance with the number of detecting switches and, therefore, a first, second, third indication lamps PL-1. PL-2, PL-3 lighten respectively. Thus, the diameters of the circular saw 16 not capable of inspecting from the outside can be recognized by the lamp indications.