A protective cap 2 is engaged with a latch 10 of a diluent container 5 so as to fix the diluent container 5 at a liquid holding position of a diluent container containing section 11. The engagement is released when the protective cap 2 is set to an open position against the engagement so as to expose an inlet 13. When the protective cap 2 is shifted from the open position to a closed position, the protective cap 2 pushes the diluent container 5 into a liquid discharge position. Thus, it is possible to preserve a diluent for a long period of time and to easily open the diluent container 5 without having to complicate the structure of an analysis apparatus.