A fastening tool (1) fastens a work piece (W) via a non-breaking-type multi-member crimping fastener (9) including a pin (91) and a collar (95). The fastening tool (1) includes an anvil (61), a pin gripping part (63), a motor (31), and a drive mechanism (planetary reduction gear (33), spindle (35), chuck (37), motion conversion mechanism (51)). The drive mechanism is driven by motive power of the motor (31), and performs a crimping step in which the pin gripping part (63) in a state of gripping a tension region (914) of the pin (91) is moved to the rear from an initial position along a drive axis (A1), whereby the collar (95) is crimped in a crimping groove of a shaft part of the pin (91) by the anvil (61). The crimping step ends when the pin gripping part (63) attains a state of being essentially incapable of rearward movement.