A sealing device with a rotation detecting element, capable of detecting rotation even when fluid such as engine oil is an object to be sealed, comprises a stationary side sealing element (seal ring) (12) fixed to the stationary side (3), a rotation side sealing element (slinger) (14) installed on the rotation side (2) and made to be in slidably and hermetically contact with the stationary side sealing element (12), and a to-be-detected disc (15) for rotation detection attached to the rotation side (2) and positioned at the atmosphere side from a sealing and sliding section (S) between the stationary side sealing element (12) and the rotation side sealing element (14), wherein the outer peripheral edge of the to-be-detected disc (15) closely faces in the radial direction the stationary side sealing element (12) side.