A connector has a first structure and a second structure. The first structure has a tubular male connector having a male-side cavity and also has a tubular female connector having a female-side cavity communicating with the male-side cavity and allowing another male connector same as the male connector to be connected to the female-side cavity. The second structure has an installation section capable of being installed on the first structure, a male lock section placed, in an installed state where the male lock section is installed on the first structure, adjacent to the male connector such that the direction of connection of the male lock section is parallel to that of the male connector, and a female lock section placed, in the installed state, adjacent to the female connector such that the direction of connection of the female lock section is parallel to that of the female connector, and allowing another male lock section same as the male lock section to be connected to the female lock section. The way of use of the first structure can be selected between use with the second structure installed on it and use without the second structure installed on it.
