To provide a chain guide structure of an engine excellent in mountability with a simple configuration.

An attachment surface 12 having a screw hole 13 is formed at the top of a boss 11 formed in a part of a cylinder head 2 between an intake cam sprocket 61 and an exhaust cam sprocket 62. A rib 14 is formed in a side part of the boss 11. A chain guide 20 formed by integrally forming an engagement projection 27 having an engagement groove 28 to be engaged with a chain guide part 25 and the rib 14, on a cylindrical base 21 having a through hole 22, is installed on the attachment surface 12 of the boss 11 while the engagement groove 28 is engaged with the rib 14. The chain guide 20 is fastened to the boss 11 with an attachment bolt 30 to be screwed in the screw hole 13 through the through hole 22.