To provide an oil leakage prevention structure and an automatic transmission preventing oil from leaking outward of a case from a portion between a rotating shaft and the case while preventing wear of an oil seal and damage thereto.

This oil leakage prevention structure and automatic transmission have: a hollow rubber tube 33 attached to a projecting portion 13b to surround the outer peripheral portion of the projecting portion 13b of the rotating shaft 13; grease 36 filled between the inner peripheral portion of the rubber tube 33 and the outer peripheral portion of the projecting portion 13b of the rotating shaft 13; and an outer lever 17 and a nut 34 attached to the projecting portion 13b of the rotating shaft 13 in order to be opposed to a transmission case 12 across the rubber tube 33 and push-pressing the rubber tube 33 toward the transmission case 12 in order to compress the rubber tube in the axis direction of the projecting portion 13b of the rotating shaft 13.