PURPOSE:To make it possible to improve linearity and to carry out sweeping small in display position error, by multiplying only one reference oblique wave signal obtained by counting a minute and equal interval reference clock pulse by the sine and the cosine of an antenna azimuth angle. CONSTITUTION:A reference clock pulse 8 is counted by a period counter 23 generating a sweep signal and the counted value 24 is subjected to analogue conversion by a D/A converter 25 to obtain a reference oblique wave signal 26. On the other hand, a sine theta and cosine theta generator 2 generates a sine theta3 and a cosine theta4 from antenna azimuth angle data 1. Because multiplication type D/A converters 27, 28 subject the reference oblique wave signal 26 to D/A conversion as reference voltage, X and Y diflection signals 29, 30 having inclination proportional to the sine theta3 and the cosine theta4 are obtained as the result. As mentioned above, because the X and Y deflection signals are generated by only one reference oblique wave signal 26 having uniform inclination, there is no refraction shown in a conventional system in both directions X, Y and, therefore the linearity of sweep brightness line is extremely good.