A mounting structure including: an outer housing having a first locking portion; a ceiling including a lamp opening portion in a central portion thereof; an inner housing including: a first locking facing portion which is locked in the first locking portion of the outer housing; and a second locking portion on and directly attached to the inner housing; and a reinforcement having a second locking facing portion which is locked on the second locking portion of the inner housing. The ceiling is fixed between the outer housing and the inner housing by locking the first locking facing portion of the inner housing in the first locking portion of the outer housing via the lamp opening portion in the ceiling. A bracket portion shaped so as to follow a shape of an upper side of the ceiling is provided along an outer circumference of the inner housing.