Automatic analyzer

An automatic analyzer, comprising:

• a photomultiplier tube;
• a board disposed vertically below the photomultiplier tube and comprising a lower board surface;
• a pressing member;
• and
• a flow cell disposed vertically below the board and comprising a upper cell surface and a lower cell surface,
• wherein the lower board surface of the board has a first protrusion portion or a first recess portion, and
• wherein the cell upper surface of the flow cell has a second recess portion or a second protrusion portion, and
• wherein the pressing member configured to contact the lower cell surface and press the flow cell vertically upward toward the board from below and fit the second protrusion portion into the first recess portion or the second recess portion onto the first protrusion portion to fit the flow cell onto the board,
• wherein the flow cell comprises the second recess portion and the second protrusion portion,
• wherein the second recess portion comprises a circumferential shape on an inner circumferential area of the upper cell surface, and
• wherein the second protrusion portion comprises a circumferential shape on an outer circumferential area of the upper cell surface.