There is provided an electromagnetic contactor unit capable of firmly connecting electromagnetic contactors without influencing outer dimensions when the electromagnetic contactors are connected to each other. The electromagnetic contactor unit connected at least two juxtaposed electromagnetic contactors (2a, 2b) with a connection piece (42). The electromagnetic contactor includes an attachment hole (41a) formed in each corner of an attachment plate portion, a piece accommodation concave portion (43) fitting a half portion of the connection piece formed above the attachment hole and accommodating within an outer dimension, and is opened to a connection surface with the adjacent electromagnetic contactor, and a locking portion (44) locking the connection piece formed in the piece accommodation concave portion. The connection piece includes a pair of engagement protrusions (42b, 42c) which are individually engaged with the adjacent attachment holes of the juxtaposed electromagnetic contactors, and a locked portion (42k) locked by the locking portion.