A power source apparatus comprising: a battery module including a plurality of battery cells; a chassis having an inner space surrounded by a plurality of wall surfaces including a first lateral wall surface, a first vertical wall surface, a second lateral wall surface, and a second vertical wall surface and storing the battery module in the inner space, the first lateral wall surface being arranged on a first side of the battery module, the first vertical wall surface being connected to the first lateral wall surface and extending toward a side opposite to the first side of the battery module, the second lateral wall surface being arranged on the side opposite to the first side of the battery module and being opposed to the first lateral wall surface, the second vertical wall surface being opposed to the first vertical wall surface; and a blower having a blowing portion to blow air, characterized in that the power source apparatus further comprises: an air introduction path formed between the first lateral wall surface and the battery module and configured to introduce the air to the battery module, the air being blown from the blowing portion, the air introduction path including: a first area positioned closer to the first vertical wall surface than to a center of the blowing portion; a second area positioned closer to the second vertical wall surface than to the center of the blowing portion; and an expanded portion expanding a separation distance (d) between the first lateral wall surface and the battery module gradually from the second area toward the first area; and a flow path to introduce air to the air introduction path, the air being blown from the blowing portion, wherein the blowing portion is arranged between the battery module and the second lateral wall surface and is closer to the second vertical wall surface than to a position at which the separation distance (d) is maximized. a battery module including a plurality of battery cells; a chassis having an inner space surrounded by a plurality of wall surfaces including a first lateral wall surface, a first vertical wall surface, a second lateral wall surface, and a second vertical wall surface and storing the battery module in the inner space, the first lateral wall surface being arranged on a first side of the battery module, the first vertical wall surface being connected to the first lateral wall surface and extending toward a side opposite to the first side of the battery module, the second lateral wall surface being arranged on the side opposite to the first side of the battery module and being opposed to the first lateral wall surface, the second vertical wall surface being opposed to the first vertical wall surface; and the first lateral wall surface being arranged on a first side of the battery module, the first vertical wall surface being connected to the first lateral wall surface and extending toward a side opposite to the first side of the battery module, the second lateral wall surface being arranged on the side opposite to the first side of the battery module and being opposed to the first lateral wall surface, the second vertical wall surface being opposed to the first vertical wall surface; and a blower having a blowing portion to blow air, characterized in that the power source apparatus further comprises: an air introduction path formed between the first lateral wall surface and the battery module and configured to introduce the air to the battery module, the air being blown from the blowing portion, the air introduction path including: a first area positioned closer to the first vertical wall surface than to a center of the blowing portion; a second area positioned closer to the second vertical wall surface than to the center of the blowing portion; and an expanded portion expanding a separation distance (d) between the first lateral wall surface and the battery module gradually from the second area toward the first area; and a flow path to introduce air to the air introduction path, the air being blown from the blowing portion, wherein the blowing portion is arranged between the battery module and the second lateral wall surface and is closer to the second vertical wall surface than to a position at which the separation distance (d) is maximized. an air introduction path formed between the first lateral wall surface and the battery module and configured to introduce the air to the battery module, the air being blown from the blowing portion, the air introduction path including: a first area positioned closer to the first vertical wall surface than to a center of the blowing portion; a second area positioned closer to the second vertical wall surface than to the center of the blowing portion; and an expanded portion expanding a separation distance (d) between the first lateral wall surface and the battery module gradually from the second area toward the first area; and a first area positioned closer to the first vertical wall surface than to a center of the blowing portion; a second area positioned closer to the second vertical wall surface than to the center of the blowing portion; and an expanded portion expanding a separation distance (d) between the first lateral wall surface and the battery module gradually from the second area toward the first area; and a flow path to introduce air to the air introduction path, the air being blown from the blowing portion, wherein the blowing portion is arranged between the battery module and the second lateral wall surface and is closer to the second vertical wall surface than to a position at which the separation distance (d) is maximized.