A component measuring apparatus for measuring the quantity and/or quality of a predetermined component in a specimen, comprising: a case including a tubular case body having a distal-end opening and a window; a detector for detecting the predetermined component, the detector being disposed in the distal-end opening of the case body and having at least a portion positioned inside the case body and having the remaining portion projecting from the case body through the distal-end opening; a sampling device mounting part disposed on a distal end portion of the detector and projecting outwardly from the detector for detachably mounting thereon a sampling device ( 500, 600) for sampling the specimen; a controller electrically connected to the detector and including a measuring unit for measuring the predetermined component, the controller having a function to control operation of at least the detector; a display having a function to display a measurement result measured by the measuring unit, for allowing the measurement result to be visually recognized through the window; a cell mounting part for mounting a cell for supplying electric power to at least the controller; a proximal-end opening disposed on the case body; a lid disposed so as to cover the proximal-end opening of the case body; and second hermetic sealing means ( 91a, 91b, 92) disposed in the proximal-end opening between the case body and the lid, wherein a housing space defined by the case body, the lid, and the detector for housing the controller, the display, and the cell mounting part is hermetically sealed by the first hermetic sealing means and the second hermetic sealing means ( 91a, 91b, 92), characterized in that the component measuring apparatus further comprises first hermetic sealing means disposed in the distal-end opening between the case and the detector; and an ejector member for removing the sampling device ( 500, 600) mounted on the sampling device mounting part from the sampling device mounting part, the ejector member being disposed outside of the detector and supported movably along axial directions of the case body, wherein the case body has an inspection through hole for inspecting the component measuring apparatus about hermetic sealing therein, the inspection through hole being sealed by a sealing member. a case including a tubular case body having a distal-end opening and a window; a detector for detecting the predetermined component, the detector being disposed in the distal-end opening of the case body and having at least a portion positioned inside the case body and having the remaining portion projecting from the case body through the distal-end opening; a sampling device mounting part disposed on a distal end portion of the detector and projecting outwardly from the detector for detachably mounting thereon a sampling device ( 500, 600) for sampling the specimen; a controller electrically connected to the detector and including a measuring unit for measuring the predetermined component, the controller having a function to control operation of at least the detector; a display having a function to display a measurement result measured by the measuring unit, for allowing the measurement result to be visually recognized through the window; a cell mounting part for mounting a cell for supplying electric power to at least the controller; a proximal-end opening disposed on the case body; a lid disposed so as to cover the proximal-end opening of the case body; and second hermetic sealing means ( 91a, 91b, 92) disposed in the proximal-end opening between the case body and the lid, wherein a housing space defined by the case body, the lid, and the detector for housing the controller, the display, and the cell mounting part is hermetically sealed by the first hermetic sealing means and the second hermetic sealing means ( 91a, 91b, 92), characterized in that the component measuring apparatus further comprises first hermetic sealing means disposed in the distal-end opening between the case and the detector; and an ejector member for removing the sampling device ( 500, 600) mounted on the sampling device mounting part from the sampling device mounting part, the ejector member being disposed outside of the detector and supported movably along axial directions of the case body, wherein the case body has an inspection through hole for inspecting the component measuring apparatus about hermetic sealing therein, the inspection through hole being sealed by a sealing member.