To inhibit deterioration in sealing performance when external force such as torsion is applied to an electric wire.

A cylindrical seal member 21 is inserted in an electric wire insertion hole 11 of a housing 7 having an electric wire 5 inserted therein and seals a gap between the outer peripheral face of the electric wire 5 and the inner peripheral face of the electric wire insertion hole 11. Sinusoidal wave-like mountains 33 and valleys 35 are formed on the inner and outer peripheral faces of the cylinder in the axial direction, and phases of the mountains 33 on one surface and the valleys 35 on the other surface are formed to match in the axial direction.