Internal combustion engine and straddle-type vehicle equipped with the engine

A single-cylinder internal combustion engine having a knock sensor mounted thereto can suppress a temperature rise of the knock sensor and at the same time detect knocking with high accuracy. An engine (10) has a cylinder block (12) having a cylinder (15) formed therein, and a cylinder head (13) connected to the cylinder block (12). On a surface of the cylinder block (12) and the cylinder head (13), one or more fins (33) protruding from the surface are provided. On the surface of the cylinder block (12), a sensor mounting boss (40) protruding from the surface and being continuous to a portion of the one or more fins (33) is provided. A knock sensor for detecting knocking is mounted to the sensor mounting boss (40).