The invention relates to a casting machine synchronizing device which comprises a bracket and is characterized in that a hold-down mechanism is arranged on the bracket and comprises a cylinder fixed on the bracket and a lever fixed on the bracket through a hinge shaft, wherein the cylinder is hinged with one end of the lever, the other end of the lever is provided with vulcanization wheels and a rotary coder which are in contact with the upper edge of a sand box, and the vulcanization wheels and the rotary coder are connected through a transmission mechanism. Because the three groups of vulcanization wheels are held down by adopting the cylinder, obtained signals are continuous and stable; due to the adoption of a tensioned flexible synchronous belt, the obtained signals are more accurate; and the cylinder with a pressure detection function is adopted to control the on or off of the synchronizing device, therefore, the reliability and the service life of the synchronizing device can be ensured.