The present invention provides a connection unit capable of accommodating nuts and showing sealing ability in a state installed on a housing.A connection unit S includes: a terminal block 100 having holes h3 at one side of for accommodating nuts n; a terminal-connecting portions 200 at least partially exposed when viewed from the other side and fixed to the terminal block 100 with the circumferences of the terminal-connecting portions 200 in tight contact with the terminal block 100; and a nut cover 300 for covering the nuts accommodated in the holes h3 for preventing the nuts n from coming off. The connection unit S further includes: guide grooves and guide ribs for restricting movement of the nut cover 300 relative to the terminal block 100; and locking hooks 116 and locking holes h5 for restricting movement of the nut cover 300 relative to the terminal block 100.