To securely expose a disk 6 to sterilization gas.

In the sterilization tester 1, an opening 3A of a culture container 3 is closed with aluminum foil 4, and the disk 6 as a tested index object is mounted on the foil. The disk 6 is covered with a cap 5, and a filter 7 for allowing penetration of the sterilization gas and prohibiting penetration of environmental bacteria is attached to a gas flowing port 5B of the cap 5. By setting the sterilization tester 1 in a sterilization chamber when the sterilization chamber is sterilized with the sterilization gas, the disk 6 is sterilized with the sterilization gas penetrating into the cap 5 through the gas flowing port 5B. After the disk 6 is taken out of the sterilization chamber, the disk 6 is fallen down into a culture solution 2 as the aluminum foil 4 is broken by a cutter 8 by screwing the cap 5 deep.