A filter includes a first case member and a second case member that are made of synthetic resin and are mutually joined to form a filter chamber, and a filter element including a filtering medium and a holding frame that is made of synthetic resin, which holds a peripheral portion of the filtering medium and is held between joining ends of the case members. Weld portions formed by laser light are provided at a contact area extending in a joining direction between the holding frame of the filter element and at least one joining end of the joining ends of the case members.