PURPOSE: To make it possible to shorten the measuring time of a noise by displaying the different signal inputs at the same time on a screen through a plurality of input terminals.

CONSTITUTION: An antenna C is provided at a place where the noise from a product does not reach and connected to an input terminal A of a spectrum analyzer G. Then, an antenna D is provided based on the measuring method specified at each time and connected to an input terminal B of the analyzer G. For example, the terminal A is held at the first screen and the terminal B is held at the second screen at the maximum degree. At this time, the images can be readily observed when the same input as that to the terminal A or the terminal B is swept by using the third screen. Since the spectrum of the same frequency generated on the first and second screens is caused by external noise, the spectrum is removed with a computer when the measurement is finished. Only the required spectrum for the specified value for each time is measured based on the remaining spectrums. Since the external noise and the noise from a product can be measured at the same time, the time can be shortened.