A synchronous detection device comprises two gears, two inductors and a microprocessor. A synchronous detection method is used for detecting synchronous rotation state of two rotating shafts, and comprises the following steps: each rotating shaft is respectively provided with the gear to cause the gear to synchronously rotate with the corresponding rotating shaft; the two inductors are provided and respectively arranged beside the gears; the rotating shaft is rotated to cause the teeth crests of the gear to pass through the inductors, the teeth crests passing through the inductors are induced;and the rotation distance difference values of various rotating shafts are calculated. The invention further provides a cutting apparatus which comprises a cutting device, the two rotating shafts andthe synchronous detection device, and the synchronous detection device is used for detecting the synchronous rotation state of the two rotating shafts. The synchronous detection device has simple structure, and the synchronous detection device and synchronous detection method have wide application range, high detection reliability and low cost, and the synchronous rotation state of the two rotatingshafts can be detected in real time by the cutting apparatus of the synchronous detection device, thus ensuring accurate cutting of sheet materials.