PURPOSE: To display a picture signal from a storage device onto a display tube, by sweep-controlling an electronic beam whose luminance is modulated, in a display tube of an oscilloscope, by a trigger sweep function and a vertical synchronizing signal obtained from an address signal.

CONSTITUTION: An address counter 14 supplies an address signal 18 to a storage device controlling circuit 8. The controlling circuit 8 applies the address signal 18 as an address signal 13 to a storage device 10, its picture signal is read out, and a read-out signal 12 impressed to a D/A converter 17. The converter 17 converts a luminance signal of each picture element from the storage device 10, to an analog signal, impresses it to a luminance signal terminal Z of an oscilloscope 16, and modulates luminance of an electronic beam. Subsequently, a carry signal of the address counter 14 is inputted as a trigger signal 20 to a trigger signal input terminal TRIG of the oscilloscope. Simultaneously, the oscilloscope can sweep-control an electronic beam of the display tube by generating a saw tooth wave by itself in its inside.