A trigger switch includes a case having a switching mechanism inside thereof and open on one side, a cover configured to be fitted inside an opening of the case to close the opening, and a trigger arranged outside of the case and configured to operate the switching mechanism by sliding operation via the plunger. An engaging depression is formed on an inner wall surface defining an opening edge portion of the case. A shoulder is formed on an outer peripheral end edge portion of the cover. An engaging projection is formed to project outward from a side surface of the shoulder to a small extent so as to be capable of engaging with the engaging depression corresponding thereto. A joint groove is formed by the inner wall surface of the opening edge portion of the case and the shoulder, and the joint groove is filled with an adhesive agent.