A lamp capable of effectively suppressing increase in the temperature of circuit devices is provided. The lamp includes: an LED module composed of LED chips; a base through which electric power is received; a lighting circuit which includes a circuit device group for generating electric power for causing the LED module to emit light using the electric power received through the base; an inner casing which is a tubular portion made of resin for housing the lighting circuit; and an outer casing which is a tubular portion for housing the inner casing. On the circumferential surface of the inner casing, a protrusion is provided which directly abuts the inner circumferential surface of the outer casing.