An in-vehicle cooling device includes: a header to be mounted so as to be adjacent to a side surface of a transformer mounted on a back side of a bottom portion of a vehicle, the header having a vertical surface along a traveling direction and a direction orthogonal to the travelling direction; a vertical-direction installed cooling pipe having both ends fixed to the header and being installed on a vertical plane orthogonal to the traveling direction; and a traveling-direction installed cooling pipe having both ends fixed to the header and being installed on a travel plane that is parallel to a horizontal plane, the vertical-direction installed cooling pipe and the traveling-direction installed cooling pipe being installed to overlap with each other in a direction orthogonal to the header.