In a general-purpose internal combustion engine connectable to operating machines such as a snowplow, a washing machine and a wood chipper having an electronic control unit that controls operation of the operating machine when connected, there are provided a signal output terminal that is installed in the electronic control unit and outputs a signal generated by the electronic control unit to the operating machine and a signal selector constituted by a personal computer that selects a signal to be outputted by the signal output terminal from among signals in response to manipulation by an operator. The engine can be easily connected with any operating machine without a complicated electronic control unit, thereby improving versatility and convenience.