A connection module includes a first assembly and a second assembly. The first assembly has a rest portion for resting thereon an exposed portion of a covered electrical wire for differential signal transmission. A cable accommodates the covered electrical wire in a jacket. The exposed portion is not covered with the jacket, exposing a covering of the covered electrical wire. The second assembly has a presser portion pressing the exposed portion rested on the rest portion against the rest portion. A position of the exposed portion is determined by combining the first assembly with the second assembly.