A device for treating the lumen of a living body includes a shaft insertable into a blood vessel, and a balloon provided on the shaft and shiftable between a deflated state and an expanded state. In the expanded state, the balloon has a recessed portion configured to form a coating chamber which is substantially blocked between an inner surface of the blood vessels and the device for treating the lumen of a living body, a discharge port provided on the recessed portion to discharge a coating substance toward the coating chamber; and a suction port provided on the recessed portion to apply a negative pressure to the coating chamber.