A transmission for an internal combustion apparatus is provided in which a parking lock mechanism is commonly formed with an upstream side portion of a power transmission system of a shift change mechanism, whereby the number of parts is reduced and the parking lock mechanism is compactly incorporated therein to achieve miniaturization of the internal combustion engine. The transmission in which a shift change mechanism performs a shift change in response to an operation of a gear selecting apparatus is configured to include a parking lock mechanism which is driven in an interlocking relationship with a working portion of the shift change mechanism, and if the shift change mechanism is set to the parking position, then a rotary shaft of the transmission is locked against rotation by the parking lock mechanism thereby restricting rotation of the rotary shaft.