PURPOSE: To insert gaskets steadily in a short period of working time without allowing unevenness, gradient, zigzagging and others to happen and without requiring skilled labor.

CONSTITUTION: A gasket insertion jig for use in insertion of sealing gaskets to joints provided between exterior members forming the exterior of a building is composed of a first base 1 and a second base 2, equipped respectively with flat parts 1b and 2b to one side thereof. A first projecting stripe 10 and a second projecting stripe 20 are erected in a specified height and are provided, connecting to each of the flat parts 1b and 2b. Both of the bases 1 and 2 are united into one piece in a doglegged shape with an obtuse angle α provided in between.