PURPOSE: To print a scale together with a measuring waveform by storing a scale into the second memory means beforehand and reading the scale.

CONSTITUTION: In a scale memory 15 of the number of the same bit as a VRAM 3, scale data corresponding to the scale of the display screen of a measuring instrument are stored beforehand. When video data VD by one screen are read into the VRAM 3, a CPU 11 outputs '0' signal, and next, the address of the VRAM 3 is successively outputted. The address is supplied in parallel from a data transfer circuit 6 to the VRAM 3 and the scale memory 15, and the data in the VRAM 3 and the data in the scale memory 15 are both read. The OR of the read data is obtained in an OR circuit 16, and the output of the OR circuit 16 is supplied to a head driving circuit 8 as printing data. Thus, onto the printing paper, the scale is printed together with the image, etc., of the display screen.