PURPOSE: To mount parts automatically and continuously by computing the coordinate values of a plurality of the positions of part placement and the coordinate values of a plurality of part placement heads previously.

CONSTITUTION: The coordinate values of a plurality of part-placement positions A, B and the coordinate values of a plurality of part placement heads 3, 4 are computed previously, both coordinate values and a predetermined movable range (d) are collated, the keeping of the part placement head within the movable range (d) is decided when the part is held and mounted at any position of part placement by the part placement head, and the result of the decision is set beforehand as control information. The optimal part placement head 3 or 4 is selected from control information and the part is held when the part is sustained, and the part is transferred and mounted. Accordingly, a plurality of the part placement heads 3, 4 are operated respectively within the predetermined movable range (d), thus automatically mounting the parts continuously.