A vehicle battery pack comprising: a battery case in which a battery module is built; an electrical component configured to convert electric power from the battery module; a duct through which an air for cooling flows; a cooling fan configured to circulate the air to the duct; and a housing which houses the battery case, the electrical component, and the duct, wherein the battery case includes: a first vertical wall extending in a first direction; a second vertical wall extending in a second direction orthogonal to the first vertical wall; and a corner portion where the first vertical wall and the second vertical wall intersect, wherein the electrical component is disposed on a lateral side of the battery case in a manner facing the first vertical wall in the second direction, wherein the duct includes: an upstream duct connected to the cooling fan; and a downstream duct that communicates with a discharge port formed on the upstream duct and that is configured to guide the air, which is guided from the upstream duct through the discharge port, to the battery case and the electrical component, characterized in that the downstream duct includes: a first downstream duct portion that extends from the corner portion along the first vertical wall, the first downstream duct portion having a downstream end that communicates with the electrical component; a second downstream duct portion that extends from the corner portion along the second vertical wall, the second downstream duct portion having a downstream end that communicates with the battery case; and a downstream duct corner portion connected to the first downstream duct portion and the second downstream duct portion on a lateral side of the corner portion, and wherein the discharge port is disposed across one of the first downstream duct portion and the second downstream duct portion, and across the downstream duct corner portion. a battery case in which a battery module is built; an electrical component configured to convert electric power from the battery module; a duct through which an air for cooling flows; a cooling fan configured to circulate the air to the duct; and a housing which houses the battery case, the electrical component, and the duct, wherein the battery case includes: a first vertical wall extending in a first direction; a second vertical wall extending in a second direction orthogonal to the first vertical wall; and a corner portion where the first vertical wall and the second vertical wall intersect, a first vertical wall extending in a first direction; a second vertical wall extending in a second direction orthogonal to the first vertical wall; and a corner portion where the first vertical wall and the second vertical wall intersect, wherein the electrical component is disposed on a lateral side of the battery case in a manner facing the first vertical wall in the second direction, wherein the duct includes: an upstream duct connected to the cooling fan; and a downstream duct that communicates with a discharge port formed on the upstream duct and that is configured to guide the air, which is guided from the upstream duct through the discharge port, to the battery case and the electrical component, an upstream duct connected to the cooling fan; and a downstream duct that communicates with a discharge port formed on the upstream duct and that is configured to guide the air, which is guided from the upstream duct through the discharge port, to the battery case and the electrical component, characterized in that the downstream duct includes: a first downstream duct portion that extends from the corner portion along the first vertical wall, the first downstream duct portion having a downstream end that communicates with the electrical component; a second downstream duct portion that extends from the corner portion along the second vertical wall, the second downstream duct portion having a downstream end that communicates with the battery case; and a downstream duct corner portion connected to the first downstream duct portion and the second downstream duct portion on a lateral side of the corner portion, and a first downstream duct portion that extends from the corner portion along the first vertical wall, the first downstream duct portion having a downstream end that communicates with the electrical component; a second downstream duct portion that extends from the corner portion along the second vertical wall, the second downstream duct portion having a downstream end that communicates with the battery case; and a downstream duct corner portion connected to the first downstream duct portion and the second downstream duct portion on a lateral side of the corner portion, and wherein the discharge port is disposed across one of the first downstream duct portion and the second downstream duct portion, and across the downstream duct corner portion.