According to an embodiment, a high-speed transmission connector includes: a row of first contacts, a row of second contacts, a row of third contacts, a row of fourth contacts, an upper housing that supports the row of first contacts, a lower housing that supports the row of second contacts, and an inner housing that supports the row of third contacts and the row of fourth contacts. The upper housing, the lower housing, and the inner housing are assembled in such a manner that the upper housing and the lower housing face each other in a vertical direction with a gap therebetween, and the inner housing is accommodated in the upper housing and the lower housing. The gap forms a slot into which a header of a device as a communicating counterpart is to be fitted.