A detection device is provided which comprises an examination flow channel for passing a fluid containing a detection object, a reference flow channel extending adjacently along the examination flow channel, an interaction film interposed between the examination flow channel and the reference flow channel for causing an interaction thereof, a light emission unit for injecting a detecting light into the reference flow channel, and a detection unit for receiving the detecting light. This device is used for recognizing the state of the detection object in the examination flow channel from deflection of the optical path of the detecting light caused by the interaction.