A total organic carbon meter including a sample introduction mechanism that includes a case in which a sample introduction and rod opening is formed; a sample introduction rod at the front end part of which a sample tray is arranged and which is inserted in the set direction through the sample introduction and rod opening; and a cover formed on the outer circumferential surface of the sample introduction rod, wherein the insertion of the sample introduction rod, on the front end part of which a sample tray has been arranged, through the sample introduction and rod opening, causes the gap between the sample introduction and rod opening and the sample introduction rod to be closed by the cover.