PURPOSE: To make a graph very easy to understand, by selecting maximum numerical data from numerical data in a memory and determining the integral value of a maximum scale of the graph on a basis of this selected value.

CONSTITUTION: When numerical data are inputted successively from a key input part 6, they are stored in a data memory area of an RAM 3. Maximum numerical data is selected from this numerical data group. A classification of a table in the RAM 3 which corresponds to the upper N-number of digits of this numerical data is discriminated, and as the result, a maximum integral scale and the number of division and the number of pitch between a minimum scale and the maximum scale are determined, and thereafter, a graph for input data is made.