Abstract: A tennis ball throwing machine which comprises a motor secured to a frame board, the output end of the motor shaft having a gear wheel securely mounted thereon, first and second transmission shaft respectively fixed to a gear wheel at one end thereof and engaged with the gear wheel of the motor, a bat pivotally attached to the first transmission shaft, one end of the bat being a hitting portion, and the other end thereof being attached to a tension spring, a cam pivoted on the second transmission shaft, a ball guiding groove being pivoted on a supporting shaft and having a portion thereof in contact with the cam to move upward, downward, leftward and rightward, a tension spring at the bottom end of the ball guide groove.