A component installing device comprises: a tray component supply section (8) having a plurality of conjointly provided tray component supply mechanisms (7) for moving selected trays (4) from a storage position (5) to a component supply position (6), according to need, thereby providing the components (2) accommodated therein for use; and a cassette component supply section (13) having a plurality of mutually aligned component supply cassettes (12) for carrying components in a tape cassette or a bulk cassette, and transporting said components to a component supply position (11), one at a time, thereby providing said components for use. Components (2) accommodated in the respective trays (4) located at the component supply positions (6) of the respective tray component supply mechanisms (7) in the tray component supply section (8), and components (2) transported to the component supply positions (11) of the respective component supply cassettes (12) in the cassette component supply section (13), are variously handled and installed at prescribed positions on a circuit board (1) by means of an installing head (21).