PURPOSE: To obtain a control circuit which may be commonly used for both fluorescent display and liquid crystal display, by providing the control circuit with such a function that a clock signal having a suitable period and a control signal for expressing a period to be displayed are issued.

CONSTITUTION: Connection is made such as shown by the solid line in the case of using a bluorescent display device 3a but is made such as shown by the chain line (a) in the case of using a liquid crystal display device 3b. In either one of cases, the same signal is issued from a control circuit 1 as a control signal Pc, but a signal converting circuit issues an output signal pd from an output terminal Tout when both terminals T1, T2 are at low level, but issues an output signal Pd' when the terminal T2 is at high level. Since an opposite phase signal with respect to a clock signal c appears at the terminal T1, an alternate voltage Va is applied to the liquid display device 3b if the electrode of the liquid crystal device is connected between the terminals T1, Tout so that the liquid crystal is energized.