A fastening tool. In the fastening tool, a top part guiding matching portion engages a top part guiding portion in a sliding fit; a pressing part guiding matching portion engages a pressing part guiding portion in a sliding fit; a lever hinged to a base part; a transmission part engages a transmission part guiding slot in a sliding fit; the transmission part is driven to slide by the pressing part, and the lever is driven to rotate by the transmission part, then the top part is driven to slide out, due to a reaction force acting on the pressing part by the transmission part and the friction between the pressing part and the base part, the pressing part remains to be self-locked by friction, which can constrain the pressing part and the top part is locked.