A fastening tool configured to fasten a workpiece via a fastener, the fastener having a pin and a cylindrical part through which the pin is inserted, the fastening tool comprising a housing extending in a front-rear direction of the fastening tool along a specified driving axis, a cylindrical fastener-abutment part held by a front end portion of the housing so as to be capable of abutting on the cylindrical part, a pin-gripping part having a plurality of gripping claws configured to grip a portion of the pin, the pin-gripping part being coaxially held within the fastener-abutment part so as to be movable in the front-rear direction along the driving axis relative to the fastener-abutment part, the pin-gripping part being configured such that its gripping force of gripping the pin is changed by movement of the plurality of gripping claws in a radial direction relative to the driving axis along with movement of the pin-gripping part in the front-rear direction relative to the fastener-abutment part; a detection-target part provided to move together with the pin-gripping part in the front-rear direction, a detection device configured to detect the detection-target part when the pin-gripping part is placed in a specified detection position in the front-rear direction, a motor, and a driving mechanism configured to be driven by power of the motor and to move the pin-gripping part rearward from an initial position along the driving axis relative to the fastener-abutment part so as to pull the pin gripped by the plurality of gripping claws and deform the cylindrical part abutting on the fastener-abutment part, thereby fastening the workpiece via the fastener and breaking the pin at a small-diameter part for breakage, the driving mechanism being further configured to move the pin-gripping part forward, after the breakage, along the driving axis relative to the fastener-abutment part so as to return the pin-gripping part to the initial position based on a detection result of the detection device, characterized in that the fastening tool is configured such that a first moving distance is adjustable, the first moving distance being a distance by which the pin-gripping part is moved from the detection position to the initial position. a housing extending in a front-rear direction of the fastening tool along a specified driving axis, a cylindrical fastener-abutment part held by a front end portion of the housing so as to be capable of abutting on the cylindrical part, a pin-gripping part having a plurality of gripping claws configured to grip a portion of the pin, the pin-gripping part being coaxially held within the fastener-abutment part so as to be movable in the front-rear direction along the driving axis relative to the fastener-abutment part, the pin-gripping part being configured such that its gripping force of gripping the pin is changed by movement of the plurality of gripping claws in a radial direction relative to the driving axis along with movement of the pin-gripping part in the front-rear direction relative to the fastener-abutment part; a detection-target part provided to move together with the pin-gripping part in the front-rear direction, a detection device configured to detect the detection-target part when the pin-gripping part is placed in a specified detection position in the front-rear direction, a motor, and a driving mechanism configured to be driven by power of the motor and to move the pin-gripping part rearward from an initial position along the driving axis relative to the fastener-abutment part so as to pull the pin gripped by the plurality of gripping claws and deform the cylindrical part abutting on the fastener-abutment part, thereby fastening the workpiece via the fastener and breaking the pin at a small-diameter part for breakage, the driving mechanism being further configured to move the pin-gripping part forward, after the breakage, along the driving axis relative to the fastener-abutment part so as to return the pin-gripping part to the initial position based on a detection result of the detection device, characterized in that the fastening tool is configured such that a first moving distance is adjustable, the first moving distance being a distance by which the pin-gripping part is moved from the detection position to the initial position.