It is an object to improve detection accuracy of an object as compared with prior arts. A flow passage (10) provided in a detection device (10) includes a substrate (1) and a covering member (2) provided at a position corresponding to the substrate (1). A covering member opening (HL2) of the covering member (2) is provided such that a substrate opening (HL1) of the substrate (1) is not covered with the covering member (2). The covering member (2) is arranged onto the substrate (1) such that a substrate capacitance and a covering member capacitance are connected in series. The covering member capacitance is lower than the substrate capacitance.