To make it possible to alter a cell length with reduction of a manufacturing cost so that a spacer can be securely positioned at a desired position, a cell includes: a pair of optical windows sandwiching a flow channel; a cell body provided with an accommodating recess and a solution introduction part and a solution deriving part; a pair of light transmitting members in the accommodating recess and forming the pair of optical windows; a spacer defining a distance between the opposing surfaces of the pair of light transmitting members; and a pressing mechanism for pressing the light transmitting members and the spacer toward the bottom surface of the accommodating recess so as to form the flow channel, wherein a positioning recess having a shape corresponding to the spacer is provided on at least one of the opposing surfaces and the spacer is fitted therein.