An illumination device for use with gas combustor, which includes an engage ring and at least one lamp. The outer circumference of the engage ring is formed with at least one pivotal seat, and the outer circumference of each of the at least one lamps is formed with a spherical shaft having the inclined angle being adjustable and pivotally connected in the pivotal seat. The illumination device is able to be rapidly connected to a conventional gas combustor, when the above two are combined as one piece, a light source of each of the at least one lamps can be turned on through adjusting the inclined angle of each of the at least one lamps relative to the engage ring, so the generated lights can be projected to the combusting location of the gas combustor to provide required illumination during the combustion operation.