An analytical device includes a plate including a first substrate having a front surface and a back surface and a second substrate facing the back surface of the first substrate such that at least one detection space observable from outside is formed between the second substrate and the back surface of the first substrate, and an adapter. The first substrate has a first port having a through hole formed through the front surface and communicated with the detection space for delivering a liquid-containing substance into the detection space, the first substrate has a second port having a through hole formed through the front surface and communicated with the detection space for discharging a liquid-containing substance or a gas from the detection space, and the adapter is attachable to and detachable from the first port and the second port, and the front surface of the first substrate without the adapter is flat.