To improve the operating frequency of every operator by selecting a display system user interface in response to the device operating capability of the operator.

The time needed for an operator to input a commodity is measured, and the device operating capability of the operator is decided based on the measured time under multistage like. Thus, the display mode of a display 19 where the display system user interfaces I are previously set in many steps and for the device operating capability of every operator is automatically switched based on the decision result. Thus, an interface I of the optimum display mode is automatically selected among those interfaces I which are previously set in each display mode in response to the device operating capability of every operator. As a result, the operating efficiency of every operator is improved.