Abstract: The present invention aims to provide a screw fastening machine for reliably switching and changing a driving force transmitting path with the seating on a work as a reference. According to the screw fastening machine in which a first pulley is connected to a first driving mechanism for applying high speed low torque drive to a drive shaft, a second pulley is fixed in an integrally rotatable manner to a transmission shaft for connecting the drive shaft, and an endless belt is interposed between the pulleys to obtain a configuration for high speed low torque drive, a second driving mechanism for low speed high torque drive is arranged on an extension of the transmission shaft, and the second driving mechanism performs the drive until a final fastening torque is reached when a screw component is seated on the work and the stall state is achieved, the final fastening torque is always reliably obtained and the work time is reduced without waste.

Abstract: The present invention aims to provide a screw fastening machine for reliably switching and changing a driving force transmitting path with the seating on a work as a reference. According to the screw fastening machine in which a first pulley is connected to a first driving means for applying high speed low torque drive to a drive shaft, a second pulley is fixed in an integrally rotatable manner to a transmission shaft for connecting the drive shaft, and an endless belt is interposed between the pulleys to obtain a configuration for high speed low torque drive, a second driving means for low speed high torque drive is arranged on an extension of the transmission shaft, and the second driving means performs the drive until a final fastening torque is reached when a screw component is seated on the work and the stall state is achieved, the final fastening torque is always reliably obtained and the work time is reduced without waste.