Patent ID: 8590424

Claim:
An automatic transmission comprising: a transmission casing which houses therein a transmission mechanism, the transmission casing having: a concave portion with which at least an oil inlet or an oil outlet communicates at an inside of the concave portion; and a first overhanging portion which extends along a surface of the transmission casing with a clearance provided between the surface and the first overhanging portion, and a filter case which is attached to the transmission casing and has therein an oil filter, the filter case having: a case body which is inserted into the concave portion; a seal member which fits onto an outer circumference of the case body and seals a boundary between an outer circumferential surface of the case body inserted into the concave portion and an inside surface of the concave portion; a first brim portion which protrudes from the outer circumferential surface of the case body and is fixed to the surface of the transmission casing; and a second brim portion which protrudes from the outer circumferential surface of the case body and is inserted into the clearance, the first brim portion and the second brim portion being arranged at different heights in an axial direction of the filter case, and the second brim portion having a second overhanging portion that serves as a rotation stopper of the case body and touches the first overhanging portion of the transmission casing when the filter case is rotated.