A lamp apparatus includes an apparatus body including a housing having a cap at one end side, and thermal conducting fins provided on an inner surface of the housing so as to extend from the one end side along the other end side thereof and project inward of the housing, a thermal radiation plate attached to the other end side of the housing in a state in which one surface side is in contact with the thermal conducting fins, a light-emitting body attached to the other surface side of the thermal radiation plate, and a lighting circuit disposed in the housing and configured to light the light-emitting body.