A root canal treatment instrument 100 continues drive of a cutting tool 5 in forward rotation drive until reaching 180 degrees, and when a load applied to the cutting tool 5 is equal to or greater than a reference load, drive of the cutting tool 5 is switched to reverse rotation drive until reaching 90 degrees. In the root canal treatment instrument 100, when a cumulative amount of rotation is equal to or greater than a reference amount of rotation, change to a drive pattern is made, forward rotation drive is continued until reaching 90 degrees, and when a load applied to the cutting tool 5 is equal to or greater than the reference load, drive of the cutting tool 5 is switched to reverse rotation drive until reaching 180 degrees.
