A parking lock mechanism of an automatic transmission includes a casing, a parking gear provided in the casing, a parking pawl engaged with the parking gear to achieve a parking lock state, and a “parking pawl holding portion” suppressing inclination of the parking pawl in an out-of-plane direction (a direction shown with an arrow DR40). A groove portion is formed in the casing. A protruding portion is provided in a sleeve fixed to the casing. A side surface of the groove portion implements a “first portion” of the “parking pawl holding portion.” A base and protruding portion are formed from a member separate from the casing, and implement a “second portion” of the “parking pawl holding portion.”