A battery unit holding device for a vehicle that holds a battery unit in place in the lower part of a body of the vehicle, comprising: a fixing part that is provided in one of the vehicle body and the battery unit; a fixed part (30, 230) that is provided in the other of the vehicle body and the battery unit and to be fixed on the fixing part; and a positioning part that is to be provided between the vehicle body and the battery unit for positioning the battery unit to the vehicle body, the fixed part (30, 230) includes a support shaft that extends in a first direction that corresponds to one of a longitudinal direction and a width direction of the vehicle body for supporting the load acting downwardly on the battery unit; characterized in that the fixing part is movable in the first direction along the support shaft while holding the support shaft at a middle position of the support shaft; the positioning part is configured to permit the fixing part to move in the first direction along the support shaft from the middle position of the support shaft when a first impact that is greater than a first preset force is applied to the vehicle body in the first direction; the positioning part includes a first bracket that is fixed on one of the vehicle body and the battery unit and a positioning pin that is fixed to the other of the vehicle body and the battery unit, and the first bracket has a first positioning hole through which the positioning pin is to be inserted; and the positioning part is configured such that, when the first impact is applied to the vehicle body in the first direction, at least one of the first positioning hole and the positioning pin is deformed or broken. a fixing part that is provided in one of the vehicle body and the battery unit; a fixed part (30, 230) that is provided in the other of the vehicle body and the battery unit and to be fixed on the fixing part; and a positioning part that is to be provided between the vehicle body and the battery unit for positioning the battery unit to the vehicle body, the fixed part (30, 230) includes a support shaft that extends in a first direction that corresponds to one of a longitudinal direction and a width direction of the vehicle body for supporting the load acting downwardly on the battery unit; characterized in that the fixing part is movable in the first direction along the support shaft while holding the support shaft at a middle position of the support shaft; the positioning part is configured to permit the fixing part to move in the first direction along the support shaft from the middle position of the support shaft when a first impact that is greater than a first preset force is applied to the vehicle body in the first direction; the positioning part includes a first bracket that is fixed on one of the vehicle body and the battery unit and a positioning pin that is fixed to the other of the vehicle body and the battery unit, and the first bracket has a first positioning hole through which the positioning pin is to be inserted; and the positioning part is configured such that, when the first impact is applied to the vehicle body in the first direction, at least one of the first positioning hole and the positioning pin is deformed or broken.