A power source apparatus having an assembled battery including a plurality of batteries of cylindrical shape arranged in a diameter direction of the battery within a case includes a holding member which holds the plurality of batteries from the diameter direction and is in contact with the inner face of the case to divide the internal space of the case into a cooling path in which a coolant flows and a gas discharge path in which gas is discharged from the battery in a battery abnormality, wherein the holding member is a solid plate member conducting heat of the battery.