To eliminate burdens that the pull-back force of an instrument hose applies to the wrist of an operator.

Normally, a hand piece 4 for dental treatment is laterally mounted on an instrument holder 6. When it is used for the dental treatment, the hand piece 4 is pulled out from the instrument holder 6. By pulling out the instrument 4 from the instrument holder 6, a motor 10 rotates to rotate a driving roller 11, the instrument hose 3 is delivered for a prescribed amount and the dental treatment is performed. When the hand piece 4 is lifted upwards, the motor 10 rotates inversely and the instrument 4 is pulled back and mounted on the instrument holder 6. A detection roller 13 is in contact with the upper part of the instrument hose 3 and pressed to the instrument hose 3 by a spring 14. When the hand piece 4 is lifted upwards, the detection roller 13 is also lifted upwards by a prescribed amount, the motor 10 rotates inversely and the instrument 4 is returned onto the instrument holder 6.