To solve the problem wherein a measured value is dispersed widely, for example, the same sample shows a different value according to a measuring date-and-time or a measurer, in measurement using a conventional contact angle measuring device.

A means is provided, wherein, when measuring a contact angle value when dropping a droplet onto the sample by image processing, the contact angle θ with lapse of time is measured, and an approximate straight line on a coordinate wherein an elapsed time t after dropping is used as a transverse axis and the contact angle θ is used as a vertical axis is formed from the acquired value, and the intercept of the approximate straight line is calculated as the value θs of the contact angle capable of evaluating surface energy of the sample.