To allow a user to be released from analyzing data, and to easily judge which parameter should be considered although there are a lot of evaluation parameters.

An off-line diagnostic system is provided with a self- characteristic measuring device 1c for measuring the step response characteristics of a control valve in a valve positioner 1, a control valve characteristic measuring device 1d for measuring the input/output characteristics of the control valve and data communication equipment 1a for transmitting the data of the step response characteristics and input/output characteristics measured in the valve positioner 1 to a host side application (host equipment) 3. In this case, a data analyzing device 1b for analyzing data obtained by the self-characteristic measuring device 1c and the control valve characteristics measuring device 1d is disposed in the valve positioner 1.