An apparatus to decrease viscosity of crude oil or bitumen and increase the rate of fractional extraction by breaking the high molecular chains in crude oil or bitumen undergoing treatment which includes a flow of crude oil or bitumen inside the treatment unit under simultaneous affection by cavitations and vibrations on different frequencies and between at least two opposite conical jets formed inside the diffusers having the same axis of symmetry and interacting with each other under the conditions of an auto-oscillations of the periodic backward flows of fluid inside each conical jet due to a periodic negative pressure inside each conical jet and the periodic negative pressure is determined in accordance with the following formulae: P a = P 0 - λ ⁢ ρ ⁢ ⁢ V 2 2 , ⁢ wherein ⁢ ⁢ V = f ⁡ ( D 4 - 2 ⁢ R ) Sh , Pa is negative pressure in backward flow between the opposite conical jets.