To prolong service life so as to reduce the frequency of replacement by providing a lighting automatic switching apparatus which is electrically connected to a circuit terminal of a heat radiation type lighting fixture and carrying a current to one filament part when the other currently used filament part stops lighting.

In an incandescent lamp 2, a first filament part A and a second filament part B, in each of which one side is used as a common terminal, are built in a glass bulb 18, while the other terminals of the first filament A and the second filament B are respectively connected to different circuit terminals A1, B1, and the common terminals are constructed as a common circuit terminal C1 connected to a base. A lighting automatic switching apparatus 4 connected to the respective terminals A1, B1, C1 carries a current to a filament 12b in the second filament part B for emitting light immediately, when a filament 12b in the filament part A stops emitting light, for example. The lighting automatic switching apparatus 4 is provided with a defective light emission detecting means which detects the failure of light emission and a switching means for switching the filament at detection of failure of light emission. In this way, failure of light emission can be prevented in an environment which has aversion to even momentary failure in light emission.