According to an installation method of a water-chamber working apparatus of the present invention, the water-chamber working apparatus includes a base that holds heat transfer tubes on a tube plate surface and is fixed to the tube plate surface, and a manipulator that is coupled with the base, suspended in a water chamber and arranged therein, and has a separable configuration. In this case, a base installing step of installing the base on the tube plate surface and a manipulator coupling step of carrying the separated manipulator (a front stage and a rear stage) into the water chamber sequentially and individually and coupling the manipulator with the base (a coupling link) are performed.