PURPOSE: To provide an excellent picture quality adjusting device capable of automatically obtaining optimum picture quality depending on the position for viewing a monitor.

CONSTITUTION: An ultrasonic wave transmission part 9 and a signal detection part 8 for detecting the reception of optical signals from a remote controller 10 and sending a command for transmitting ultrasonic wave signals to the ultrasonic wave transmission part 9 are provided inside the monitor 11 and an ultrasonic wave reception part 5, the signal detection part 4 for detecting the reception of ultrasonic waves and a time measuring part 3 for measuring the time from the time when the optical switch 1 of the remote controller is pushed until the reception of the ultrasonic waves is detected are provided inside the remote controller 10. By connecting the output of the time measuring part 3 to a light emitting part 2, the distance between a viewer and the monitor is measured by sending the time information output of the time measuring part 3 to the monitor 11 and the optimum picture quality corresponding to the distance can be automatically obtained without the need of deliberately adjusting the picture quality manually.