To shorten a measuring interval, in a sensor using total reflection attenuation by a surface plasmon or the like using two-dimensional imaging means.

A two-dimensional CCD imaging element 40 is a full frame type imaging element, a lateral direction of an array of vertical transfer CCDs is in parallel to a face including incident light and reflection light with respect to an interface 12a of a light beam 30, and an output is executed under the condition where charges of only the vertical transfer CCDs arrayed vertically are summed up, that is, after so-called binning treatment. When detecting intensity of the light beam 30 total-reflected on the interface 12a by the two-dimensional CCD imaging element 40, a component in every of respective reflection angles is photoreceived by the array of the vertical transfer CCDs. When reading out a signal from the two-dimensional CCD imaging element 40, a reading time is shortened and a noise is reduced by executing the vertical directional binning treatment.