The invention seek to enable to share main components other than a tightening unit even in use for different effective lengths corresponding to ranges of tightening torques. There are provided: a tightening unit 10 such as a ratchet; a housing 20 having a two-divided structure including a front side cover part 21 and a back side grip part 22 ; a strain body 30 provided inside the housing 20 and replaceably coupling the tightening unit 10 thereto; a distortion sensor 40 , provided to the strain body 30 , for detecting the distorted amount of the strain body 30 due to the tightening force of thetightening unit 10 ; a microprocessor chip 100 having functions including computing the tightening torque of the tightening unit 10 based on torque reference values prepared in advance and detectionresults of the distortion sensor 40 ; and an output unit 300 for outputting such as the tightening torque.