To display data along a purpose by incorporating a function of arbitrarily selecting time base scaling data as a means for setting a display format.

A numeric value for controlling a time base scaling data controller 10 is set at an arbitrary time base scale by using a key of an operation panel 11 by an operator. The data calculated here is displayed via a CPU 2 and a data write controller 5. The controller 10 is separated, and may be present in part of the CPU 2. Thus, since the controller 10 for arbitrarily selecting the scaling data, not only a viewpoint of time and number of data but also scale of a traverse axis can be arbitrarily selected.