A blower unit includes a casing defining a first passage and a second passage, a first internal-external air switching member, a second internal-external air switching member, and a partition defining an opening. During a two-layer internal/external air mode, the first internal-external air switching member opens an external air inlet and closes an internal air inlet and the second internal-external air switching member closes the external air inlet and opens the internal inlet, so that the external air is directly introduced into the first passage through the external air inlet and the external air in the second passage is introduced into the first passage through the opening of the partition and the internal air is directly introduced into the second passage through the internal air inlet and the internal air in the first passage is introduced into the second passage through the opening of the partition.