A probe which is configured for a treatment device which is configured to treat a body tissue using ultrasonic vibration, includes a base member which includes a base surface defined by a longitudinal direction and a width direction shorter than the longitudinal direction and which is a vibration-retardation member configured to hardly transmit the ultrasonic vibration, a waveguide main body which has a width smaller than a width of the base surface in a width direction, protrudes with respect to the base surface, and is extended along the longitudinal direction of the base surface, and an end effecter which is provided at a tip end portion of the waveguide main body and which is configured to treat the body tissue by the ultrasonic vibration transmitted through the waveguide main body.