Disclosed is an opening angle regulating device of a side door for a heavy equipment, which is provided between a door frame and the side door to regulate an opening angle of the side door. The opening angle regulating device includes a rod whose one end is rotatably fixed onto the door frame, and a bracket fixed onto the side door, having a guide rail slidably fixed to the other end of the rod depending on opening and closure of the side door, the guide rail having a groove that fixes the other end of the rod if the side door is opened at a predetermined angle. Preferably, the opening angle of the side door is regulated as the position of the groove is adjusted on the guide rail.