To provide an accurate and simple method of picking up and detecting a malfunction during a measuring operation of a measuring device specifying a measured variable by measurement of an output amount as a function of a known input amount.

The input amount is variable, output amounts corresponding to respective input amounts are measurable, and when the output amounts measured in various different input amounts are deviated by a threshold over values of output amounts expected by the function between input amounts and output amounts, the malfunction of the measuring operation of the measuring device can be detected.