The invention relates to an automatic lubricating device. The automatic lubricating device is composed of an oil injecting device, a piston device, a base, a timing control device and a swinging device, wherein the oil injection device comprises an oil cup, the oil cup is connected with the piston device through a flexible oil pipe, and the oil cup provides lubricating liquid; the piston device and the swinging device are connected together in an interference fit mode, the swinging device is movably installed on the base and can rotate around the base, the rear end of the swinging device is connected with the timing control device installed on the base, and the timing control device is used for controlling the movement of the swinging device. According to the automatic lubricating device,the mechanical power of the rotation of a gear can be utilized, grease injection can be performed spontaneously, operation can be automatically stopped after working is carried out for a certain time,and idling dry grinding is avoided.