provided between the protruding sections 570 with the fixed screws 574 the holding member attaching unit 551 is allowed to protrude from the surface of the sample tray 550 so as to maintain the container holding member 572 at an appropriate height so as to secure the container 512 and the lid 519 here the container holding member 572 made of the plate spring and the surface of the sample tray 550 are made substantially in parallel with each other as shown in fig6 the lid 518 includes an edge portion 519 and a center portion 520 and the edge portion 519 and the center portion 520 can be separated from each other the center portion 520 has an opening 520 a with a cover glass 521 being fixed thereon in a manner so as to cover the opening 520 a moreover the edge portion 519 has an opening 519 a so that when the center portion 520 is attached to the edge portion 519 the center portion 520 plugs the opening 519 a the peripheral portion of the opening 519 a of the edge portion 519 is processed into a tapered shape that expands downwards and the container holding member 572 is designed to press the portion of the edge portion 519 formed into the tapered shape with this arrangement the container holding member 572 allows the container 512 and the lid 518 to be maintained on the sample tray 550 in a stable manner upon securing the container 512 and the lid 518 in a state where the lid 518 is mounted on the container 512 the container 512 and the lid 518 are inserted onto the depressed portion 570 from the outer peripheral side of the sample tray 550 in this case the.