A stud welding apparatus has a welding jig, guide frames and a cartesian coordinate type robot. This robot has a travelling frame, a robot main body, an elevating arm and a stud welding gun. Power supply passages are provided on the travelling frame, the robot main body and the elevating arm, respectively, such that electric power can be supplied from a welding power source to the stud welding gun via these power supply passages. The power supply passage provided on the travelling frame is formed in a first power supply bar which is fixed to the travelling frame and is elongated in a horizontal direction. A pressure type first power supply joint is provided on the robot main body and urges a contact member to be connected to the power supply passage provided on the robot main body into contact and away from the first power supply bar by means of a cylinder. The power supply passage provided on the elevating arm is formed in a second power supply bar which is fixed to the elevating arm and is elongated in a vertical direction. A pressure type second power supply joint is provided on the robot main body and urges a contact member to be connected to the power supply passage provided on the robot main body into contact and away from the second power supply bar by means of a cylinder.