To easily pass through a cord to a cord fastener.

For this jig for passing through a cord to the cord fastener, an assembly tool main body 1 provided with a first abutted part 10 abutted to the insertor of the jig of the cord and a second abutted part 20 abutted to the receiving body of the jig facing the first abutted part 10. As for the opposing surfaces 11 and 21 of both of the first abutted part 10 and the second abutted part 20, one is provided with a part inclined to the other and thus, an area for gradually narrowing an interval of both is provided between the first abutted part 10 and the second abutted part 20. Thus, by abutting the insertor to the first abutted part 10, abutting the receiving body to the second abutted part 20 and sliding the cord fastener in a direction for narrowing the interval of both, the insertor is pushed inside the receiving body and the positions of the opening part of the receiving body and the through-hole of the insertor are matched. The need of pressing the insertor with a finger as before while matching the positions is eliminated.