There is provided a lock structure of two articles which are attached to each other by fitting one article on the other article. The lock structure includes a lock arm formed at one of the two articles, and an arm reception portion which has a retaining portion for retaining engagement with the lock arm, and is formed at the other of the two articles. During the time when the one article is attached to the other article, the lock arm is brought into abutting engagement with the arm reception portion, and is elastically deformed to slide past the retaining portion, and becomes engaged with the retaining portion. The arm reception portion has a guide portion extending to the retaining portion, and a distal end portion of the lock arm is received between the guide portion and an outer surface of the other article.