A device for distributing a poly-phase mixture having a gas phase and liquid phase which mixture is in downflow mode through at least one bed of granular solid. The device has at least one tray (P) located above one of the beds of granular solid. It further has mixer conduits (21) for the liquid and gas phases, each conduit having an upper cross section for flow (22) allowing the passage of the majority of the gas phase, and a lower cross section for flow (23) allowing the mixture formed inside the conduits to communicate with a bed of granular solid. The mixer conduits (21) also having one or more lateral cross sections for flow (26) over at least a portion of their height to allow the passage of the liquid phase and possibly a minor portion of the gas phase inside the mixer conduits. The device also has a jet breaker type dispersive system (28) having a controlled porosity disposed below the lower cross section for flow (23) and above the bed of granular solids. The distribution device being such that at least a portion of the perimeter of the dispersive system is provided with rims (100) or (101).