To immediately display accuracy during measurement to require no calculation for the accuracy.

A memory 20 having accuracy information and a sensor for detecting ambient conditions (a temperature, humidity) are added to a conventional measuring instrument. Corresponding accuracy information is read out by requirement from an accuracy display key 24 based on a content of a control signal 34 for indicating a measuring item and a switching range and the ambient conditions, so as to calculate en error and to display it together with a measured value concurrently. Miscalculation is eliminated and a measuring time is shortened thereby.