To provide an oil filter capable of protecting an filter element and an inner tube by relieving a hydraulic pressure applied to the filter element and the inner tube in the oil filter of a diesel engine.

In this oil filter, the filter element formed by disposing the inner tube therein is stored in a filter housing through a center bolt and an oil filtrated by the filter element is returned from the small hole of the inner tube to an oil pan through the restriction hole and the center bolt oil passage of the center bolt. A bypass flow passage bypassing the oil flowing into the filter housing to the inside of the inner tube is formed in the oil filter. A first bypass valve opening the inlet side of the bypass flow passage by the hydraulic pressure of the oil flowing therein in starting the engine after maintenance and a second bypass valve opening the outlet side of the bypass flow passage to the inside of the inner tube by the hydraulic pressure of the oil flowing down the bypass flow passage are installed in the bypass flow passage.