Abstract: An automatic transmission includes: a differential mechanism which includes a ring gear; a case which forms a differential chamber that houses the differential mechanism; and an oil pan which is fitted to the case, and which stores oil. The differential chamber includes a first space in which the oil supplied from the oil pan is gathered, and a second space which is formed on the opposite side of the first space with respect to the ring gear in the direction in which the rotational axis of the ring gear extends, and which is communicated with a space inside the oil pan. An oil passage, through which the oil is introduced from the first space to the second space, is formed in the case. The oil passage is formed in a bottom portion of the differential chamber.