To provide an instrument for expanding root canal capable of more hygienically executing root canal expanding operation by efficiently pouring chemicals or cleaning water into a root canal during the operation for expanding root canal.

The instrument 100 for expanding root canal includes an air circuit 101 and a water circuit 102. The water circuit 102 communicates with a water discharge port 61 which opens on the distal end of a head 60, and the air circuit 101 opens on the periphery of a hand piece 50 and communicates with one end of a chemical tank 80 detachably attached to the outside of the hand piece 50. A root canal expanding bar 70 is rotatably held in a liquid pouring holder 90 for supplying a liquid into the bar, and is selectively coupled to a liquid discharge port 83 of the chemical tank or the water discharge port 61 of the head through a tube 91 or 92.