Patent ID: 8231644

Claim:
A torque wrench used in attachment and detachment of an ultrasonic vibrator and an ultrasonic probe of an ultrasonic treatment instrument, comprising: an arm portion which is held by a user; and a head portion which is provided on a distal end portion of the arm portion so as to be integral with the arm portion, and which is configured to releasably engage with an engagement portion disposed on the ultrasonic treatment instrument and to transmit torque to the engagement portion, wherein the head portion includes an engaging portion covering an outer peripheral surface of the engagement portion and capable of engaging with the engagement portion, a slit formed by cutting a part of a peripheral wall surface of the engaging portion, a protuberance which protrudes inward from the peripheral wall surface of the engaging portion, and which meshes with an interlocking portion formed on the outer peripheral surface of the engagement portion and having a top position and a bottom position, the protuberance moving the interlocking portion from the bottom position toward the top position when the torque is transmitted to the engagement portion in a rotating operation such that the ultrasonic probe and the ultrasonic vibrator are threadedly engaged with each other, and the protuberance including a slope the height of projection, from the peripheral wall surface, of which gradually increases along the circumference of the peripheral wall and which is oriented in a direction of rotation when the torque is transmitted to the engagement portion in the rotating operation such that the ultrasonic probe and the ultrasonic vibrator are threadedly engaged with each other, and a stop surface extending in radial directions of the engaging portion, and an elastically deformable portion configured to cause at least one of two opposite side portions of the slit to be elastically deformed so that the slit is widened until the protuberance reaches the top position of the interlocking portion such that a preset value is reached by the torque applied from the engaging portion, and configured to cause the at least one of the two opposite side portions of the slit to be elastically restored when the protuberance gets beyond the top position of the interlocking portion such that torque higher than the preset value is prevented from being applied to the engagement portion to the engagement portion with the protuberance in mesh with an interlocking portion formed on the outer peripheral surface of the engagement portion.