Electric-component mounting system having device for changing spacing distance between mounting units of the system

An electric-component mounting system for mounting a plurality of electric components onto a circuit board. The system includes a plurality of electric-component mounting units which are arranged in a predetermined direction with a spacing distance between each adjacent pair of the electric-component mounting units. Each of the electric-component mounting units includes (a) a board holding device which is capable of holding the circuit board in a predetermined position, (b) a component mounting device which is capable of mounting the electric components onto the circuit board held by the board holding deice, and (c) a component supplying device which is capable of supplying the electric components to the component mounting device. The system further includes a spacing-distance changing device capable of changing the spacing distance.