A tray filling machine, comprising: a first conveying device, structured so as to transport a plurality of items arranged in one or more distinct rows, between a loading position and an unloading position along a direction of transport; a second conveying device, structured so as to transport a tray on a movement plane arranged in the proximity of the unloading position of the first conveying device beneath the first conveying device; said first and second conveying device (2,3) are synchronized in relation to each other in a manner such that the items and the tray transit contemporaneously at the unloading position and the items can be arranged on the tray, said machine further comprising a synchronization device; characterized in that: said first conveying device comprises one or more mobile lanes (21, 22), each lane being structured so as to advance a single row of items; the mobile lanes (21, 22) are interrupted at the unloading position and the items conveyed thereon are transferred from the first conveying device to the second conveying device leaving the mobile lanes (21, 22) by falling; the synchronization device is structured so as to time the advancement of the items on the first conveying device with the advancement of the tray carried out by the second conveying device in a manner such that the items and the tray transit contemporaneously at the unloading position and the items can be arranged on the tray; the synchronization device comprises a first stop element that is mobile between an active position, wherein it blocks advancement of the items along the first conveying device, and an inactive position, wherein it permits advancement of the items along the first conveying device; the synchronization device comprises a second stop element that is located upstream of the first stop element and is mobile between an active position, wherein it blocks advancement of the items along the first conveying device, and an inactive position, wherein it permits advancement of the items along the first conveying device; the first and second stop elements are synchronized with respect to each other in a manner such that when one is in its respective active position, the other is in its respective inactive position, and vice versa. said first conveying device comprises one or more mobile lanes (21, 22), each lane being structured so as to advance a single row of items; the mobile lanes (21, 22) are interrupted at the unloading position and the items conveyed thereon are transferred from the first conveying device to the second conveying device leaving the mobile lanes (21, 22) by falling; the synchronization device is structured so as to time the advancement of the items on the first conveying device with the advancement of the tray carried out by the second conveying device in a manner such that the items and the tray transit contemporaneously at the unloading position and the items can be arranged on the tray; the synchronization device comprises a first stop element that is mobile between an active position, wherein it blocks advancement of the items along the first conveying device, and an inactive position, wherein it permits advancement of the items along the first conveying device; the synchronization device comprises a second stop element that is located upstream of the first stop element and is mobile between an active position, wherein it blocks advancement of the items along the first conveying device, and an inactive position, wherein it permits advancement of the items along the first conveying device; the first and second stop elements are synchronized with respect to each other in a manner such that when one is in its respective active position, the other is in its respective inactive position, and vice versa.