To enable a reflection type liquid crystal display device to perform the display with sufficient luminance even when the irradiation quantity of outer rays of light is a little and also to suppress the power consumption of the device.

A front light 6 becoming an auxiliary light at the time the irradiation quantity of the outer rays is a little is provided at the front surface of a reflection type liquid crystal display device 5. The irradiation quantity of the outer rays is detected with the irradiation light quantity sensor 12 provided in a pen with sensor 11. The luminance of information to be displayed on the display 5 is detected with the luminance sensor 13 provided at the tip of the pen 11. Then, the lighting/turning off of the light 6 or a luminance level at the time of the lighting is adjusted by judging luminance data and the data of the irradiation quantity. When a reference luminance changing switch 15 is operated, the lowest necessary luminance can be changed. When a front light lighting/turning off changeover switch 14 is operated, the forced lighting/ turning off is to be made possible too.