A sample heating device comprising: a heating furnace that includes within itself a space for housing a sample boat holding a sample to be heated and heats the sample held in the sample boat inserted into the space; a sample boat rack on which the sample boat is placed; a mounting port which communicates with the space inside the heating furnace and which has an opening in its upper face and to which the sample boat to be subjected to heating treatment in the heating furnace is mounted by introducing the sample boat through the opening so as to rest on a sample boat resting portion; a sample boat introducing mechanism that introduces the sample boat resting on the sample boat resting portion into the heating furnace; a sample boat conveying portion that moves in a direction in a horizontal plane and in a vertical direction, wherein the sample boat conveying portion holds the sample boat placed on the sample boat rack, and mounts the sample boat to the mounting port; and an opening/closing cover provided to be movable in a horizontal direction between a position above the opening of the mounting port and a position displaced from the position above the opening of the mounting port; and a cover sliding mechanism, characterized in that the cover sliding mechanism includes a guide rail that is attached to the opening/closing cover and is inclined with respect to the vertical direction, wherein the guide rail is configured to engage with a part of the sample boat conveying portion when the sample boat conveying portion comes to a predetermined position in the horizontal plane to allow the part of the sample boat conveying portion to slide along the guide rail such that up and down movement of the sample boat conveying portion causes the opening/closing cover to move in the horizontal direction, wherein the guide rail is inclined in such a direction as to move the opening/closing cover towards the position directly above the opening of the mounting port according to the downward movement of the sample boat conveying portion such that the opening/closing cover is provided at the position directly above the opening of the mounting port when the sample boat conveying portion comes to a predetermined height. a heating furnace that includes within itself a space for housing a sample boat holding a sample to be heated and heats the sample held in the sample boat inserted into the space; a sample boat rack on which the sample boat is placed; a mounting port which communicates with the space inside the heating furnace and which has an opening in its upper face and to which the sample boat to be subjected to heating treatment in the heating furnace is mounted by introducing the sample boat through the opening so as to rest on a sample boat resting portion; a sample boat introducing mechanism that introduces the sample boat resting on the sample boat resting portion into the heating furnace; a sample boat conveying portion that moves in a direction in a horizontal plane and in a vertical direction, wherein the sample boat conveying portion holds the sample boat placed on the sample boat rack, and mounts the sample boat to the mounting port; and an opening/closing cover provided to be movable in a horizontal direction between a position above the opening of the mounting port and a position displaced from the position above the opening of the mounting port; and a cover sliding mechanism, characterized in that the cover sliding mechanism includes a guide rail that is attached to the opening/closing cover and is inclined with respect to the vertical direction, wherein the guide rail is configured to engage with a part of the sample boat conveying portion when the sample boat conveying portion comes to a predetermined position in the horizontal plane to allow the part of the sample boat conveying portion to slide along the guide rail such that up and down movement of the sample boat conveying portion causes the opening/closing cover to move in the horizontal direction, wherein the guide rail is inclined in such a direction as to move the opening/closing cover towards the position directly above the opening of the mounting port according to the downward movement of the sample boat conveying portion such that the opening/closing cover is provided at the position directly above the opening of the mounting port when the sample boat conveying portion comes to a predetermined height.