PROBLEM TO BE SOLVED: To provide a mirror surface angle adjustment device for restraining the occurrence of a malfunction.SOLUTION: A sidewall part 22 of a base 20 comprises an annular projection 83 projecting to the inside from an opening end part 82 of he sidewall part 22. The annular projection 83 slidably contacts with a third convex surface 81. Among the sidewall part 22 of the base 20, a part except for the annular projection 83 does not contact with the third convex surface 81. With such a constitution, a clearance of communicating with an external space is not formed between the third convex surface 81 of a tilting member 40 and the sidewall part 22 of the base 20. That foreign matter existing in the external space checks sliding operation of the tilting member 40. can be avoided thereby. Thus, the occurrence of a malfunction of a mirror surface angle adjustment device 10 can be restrained.
