A passage detection apparatus is configured to detect the change in the properties (propagation state of sound wave, dielectric constant, etc.) of a specific space, which changes according to the passage of an object in the specific space and the size of the object. The passage detection apparatus includes a pair of detection units configured to transmit and receive signals to and from an external device. The specific space is formed by the space between the first detection unit and the second detection unit. The first detection unit is supported by a first substrate. The second detection unit is supported by a second substrate that is parallel to the first substrate, and arranged at the position corresponding to the first detection unit supported by the first substrate.