PURPOSE: To obtain a small-sized, inexpensive oscillating device by putting plural crystal oscillators in partial charge of a necessary temperature range respectively, and switching plural oscillator outputs according to ambient temperature on the basis of the information of a sensor which detects the temperature.

CONSTITUTION: A crystal oscillator 1 is in operation firstly and a controller 5 receives information on it from a temperature sensor 4. Then when the environmental temperature varies to about +30°C, the crystal oscillator 1 reaches the upper limit of its charge range. Then, the controller 5 switches an output changeover switch 3 from the crystal oscillator 1 to a crystal oscillator 2 and sends an output to an unshown load such as a radio equipment body. Then when the environmental temperature drops to about +20°C, the controller 5 sends a switching signal to the changeover switch 3 to switches the crystal oscillator 2 to the crystal oscillator 1, and sends an output to the radio equipment body from an output terminal 6. In this case, the operations ranges of the crystal oscillators 1 and 2 overlap each other between about +20 and +30°C, so even when the environmental temperature fluctuates frequently between both temperatures, stable switching operation is performed.