in the housing 11 is disposed in the waterproofing groove portion 15 of the introduction portion 13 next the covered wire 17 having the annular waterproofing member 19 provided on the outside periphery thereof is inserted into the waterproofing groove portion 15 and at the connection portion 18 the terminal portion 16 is overlaid with the covered wire 17 so that the waterproofing member 19 and covered wire 17 are placed at the rear end of the waterproofing groove portion 15 next the opening of the top of the waterproofing groove portion 15 is closed by the cover 24 at this time the fusing portions 27 of the cover 24 are made into contact with the fusing portions 23 of the introduction portion 13 the connecting protrusions 28 are made into contact with the terminal portions 16 of the waterproofing groove portions 15 and upper portions of the connection portions 18 of the covered wires 17 further the waterproofing protrusions 29 are made into contact with upper portions of the waterproofing members 19 inserted in the waterproofing groove portions 15 with this condition the introduction portion 13 is subjected to ultrasonic vibration by applying ultrasonic vibration to the introduction portion 13 the fusing portions 27 of the cover 24 and fusing portions 23 of the introduction portion 13 are melted so that they are fused with each other because the covering portion 21 of the connection portion 18 of the covered wire 17 is.