The static laminar mixing device for mixing media of widely different viscosities has two mixers of different cross-sections arranged one after the other with the cross-section of the first mixer being smaller than the second mixer. An admixing device for metering additive of lower viscosity than the medium of the main flow is also provided. This admixing device has a plate which defines a converging orifice for passage of the main flow and additive therethrough into the first mixer while a nozzle is aligned with the orifice for adding the additive flow.