An internal combustion engine allows easy installment of a support that pivotally supports a rocker arm while preventing fretting wear due to rising of the support. The internal combustion engine includes the support, at least a portion of which is located in a hole of a cylinder head, a rocker arm that is pivotally supported on the support, and a ball plunger that secures the support inside the hole. The ball plunger includes a spring seat that contacts with the support, a ball that contacts with the cylinder head, and a spring interposed between the spring seat and the ball.