A host connector includes a connector insulator having a slot allowing detachable insertion of a plug connector of a module, a first contact terminal group including contact terminals arranged inside the connector insulator and each brought into contact with a contact pad on one side at a connection end of the plug connector, and a second contact terminal group including contact terminals each brought into contact with a contact pad on another side opposed to the aforementioned contact pad. The first contact terminal group includes grounding sub-contact terminals arranged inside slits of the connector insulator, grounding main contact terminals supporting the grounding sub-contact terminals, and signal contact terminals. Contact portions of each grounding main contact terminal and of each signal contact terminal having the same shape are arranged on a common straight line, and the signal contact terminals are disposed between the grounding main contact terminals.