PURPOSE: To realize liquid crystal display with stable display quality in a wide range of temperature by controlling the output voltage of an output terminal which controls a liquid crystal display board by a CPU.

CONSTITUTION: A constant frequency at certain temperature is inputted from a temperature measuring circuit 101 to a flip-flop 110, and the frequency is measured. A measured result is read in the CPU 107 by using a data bus 109 by the control of the CPU 107, and it is compared with data stored in a ROM 108, then, the present temperature is decided. A signal to select the voltage required to keep the display quality appropriately from the output voltage of a power source 102 based on a decision result is outputted to a selection circuit 103. The output terminal 105 outputs a driving signal generated at a driving circuit 104 with a supplied voltage to the liquid crystal display board 106. In other words. it is possible to vary the voltage which drives the liquid crystal display board 106 according to the change of temperature even when it is changed.