An air conditioner for a vehicle includes a casing that forms an air passage through which air flows, a blower fan to blow out air, and a heating device to heat air. The casing includes a passage portion through which air flows, a warm air passage that allows air to flow to the heating device, and a bypass passage that allows air to bypass the heating device. A width dimension of the passage portion in a second direction is larger than that of the heating device in the second direction, and is smaller than a height dimension of the passage portion in a first direction.