State detecting device

There is provided a raindrop detecting device using a light-emitting element and a light-receiving element, which can accurately detect a change of a received light signal in a wide dynamic range regardless of a high or low level of the received light signal. A light-receiving current of a photo diode as the light-receiving element is converted by a current to voltage conversion circuit, and a peak of the voltage is input to a range switching amplifying circuit from a peak hold circuit. The range switching amplifying circuit is configured such that a reverse input terminal of an operational amplifier is connected to a control terminal of a control component via a resistance and the control terminal is switched to Hi and Lo, thus outputting a Hi range amplification result Vout (H) and a Lo range amplification result Vout (L) that are offset from each other by Vos. The control component selects the output that is not saturated from a possible output range of the operational amplifier out of Vout (H) + Vos or Vout (L) to be used for determination on presence/absence of raindrops.