An automatic machine for applying a flexible spacer profile, preferably made of expanded synthetic material, on at least a first glass sheet designed to subsequently mate with at least one second glass sheet so as to compose the insulating glazing, the machine comprising: conveyors with a substantially vertical arrangement which include conveyance devices provided with support and traction means for acting on the lower edge of a glass sheet and with sychronous transmission means which are provided so for acting on a face of the glass sheet along a horizontal axis (x) by way of a synchronous motor thereof; a carriage with a synchronous translational motion along a vertical axis (y), that is actuatable in motion by way of a synchronous motor thereof and is provided with an application head with a synchronous rotary motion around a rotational axis (φ) defined by a shaft actuatable by means of a further synchronous motor of said carriage; and wherein said head accommodates means (304a, 304b) for synchronous traction actuatable by way of synchronous motors (305a, 205b) and means (303a-303d) for guiding the spacer profile that arrives from a reel the unwinding of which is actuatable in an adjusted manner; a plurality of reels, said reel which contains a flexible spacer profile, being one of said plurality of reels; each reel of said plurality of reels being provided with a corresponding unwinding unit, with a corresponding optional auxiliary unit and a corresponding transfer unit, containing and guiding the flexible spacer profile, said units (400, 500, 600) constituting a respective feeder assembly for a respective said reel which contains the flexible spacer profile; a guiding or spacing of the flexible spacer profile to and from the synchronous traction means (304a, 304b) of the application head for changing a reel being performable by way of said transfer unit that can be for example of a type with jaws (601, 602) which constitute grippers, moved by a pneumatic or electric actuator, said application head being provided with its own said synchronous traction means (304a, 304b), the machine being characterized in that said feeder assembly (400, 500, 600) is arranged on a magazine which is constituted by a footing provided with movable sliders (702a, 702b) on which said feeder assembly (400, 500, 600) can be coupled and can be uncoupled and can be guided to said application head, said application head, by way of said carriage, being engageable with a respective one of said feeder assemblies (400, 500, 600) by way of engagement means, such as bushes (203a, b, c) which are adapted to mate with pins (709a, 709b) being actuatable for said sliders (702a, 702b); and the flexible spacer profile being feedable to the glass sheet along a path that winds around the rotation axis (φ) of the application head. conveyors with a substantially vertical arrangement which include conveyance devices provided with support and traction means for acting on the lower edge of a glass sheet and with sychronous transmission means which are provided so for acting on a face of the glass sheet along a horizontal axis (x) by way of a synchronous motor thereof; a carriage with a synchronous translational motion along a vertical axis (y), that is actuatable in motion by way of a synchronous motor thereof and is provided with an application head with a synchronous rotary motion around a rotational axis (φ) defined by a shaft actuatable by means of a further synchronous motor of said carriage; and wherein said head accommodates means (304a, 304b) for synchronous traction actuatable by way of synchronous motors (305a, 205b) and means (303a-303d) for guiding the spacer profile that arrives from a reel the unwinding of which is actuatable in an adjusted manner; a plurality of reels, said reel which contains a flexible spacer profile, being one of said plurality of reels; each reel of said plurality of reels being provided with a corresponding unwinding unit, with a corresponding optional auxiliary unit and a corresponding transfer unit, containing and guiding the flexible spacer profile, said units (400, 500, 600) constituting a respective feeder assembly for a respective said reel which contains the flexible spacer profile; a guiding or spacing of the flexible spacer profile to and from the synchronous traction means (304a, 304b) of the application head for changing a reel being performable by way of said transfer unit that can be for example of a type with jaws (601, 602) which constitute grippers, moved by a pneumatic or electric actuator, said application head being provided with its own said synchronous traction means (304a, 304b), the machine being characterized in that said feeder assembly (400, 500, 600) is arranged on a magazine which is constituted by a footing provided with movable sliders (702a, 702b) on which said feeder assembly (400, 500, 600) can be coupled and can be uncoupled and can be guided to said application head, said application head, by way of said carriage, being engageable with a respective one of said feeder assemblies (400, 500, 600) by way of engagement means, such as bushes (203a, b, c) which are adapted to mate with pins (709a, 709b) being actuatable for said sliders (702a, 702b); and the flexible spacer profile being feedable to the glass sheet along a path that winds around the rotation axis (φ) of the application head.