PURPOSE: To easily adjust the orientation of a parabolic antenna by providing a maximum value displaying section and current value displaying section.

CONSTITUTION: A voltage limit circuit 32 for protection is connected with the input terminal 31 for inputting receiving levels of a digital display device 3 connected with the level check terminal 1a of a receiver 1 for receiving direct broadcasting by satellite. The output voltage of the circuit 32 is fetched to a CPU 34 after the voltage is converted into a digital signal and the highest received voltage value in a memory 35 is updated and recorded. A digital display section 36 is provided with a highest value displaying section 361 for displaying the highest voltage value and a current value displaying section 362 for displaying the current voltage value in real time. Therefore, the past highest voltage value is displayed in the displaying section 362 by updating while a parabolic antenna is adjusted. Thus the position where the antenna can output the highest value can be found easily when the antenna is adjusted and fine adjustment, etc., can also be performed on the antenna.