EN
An almost cosymplectic (κ,μ,ν)-space is by definition an almost cosymplectic manifold whose structure tensor fields φ, ξ, η, g satisfy a certain special curvature condition (see formula (eq1b)). This condition is invariant with respect to the so-called 𝓓-homothetic transformations of almost cosymplectic structures. For such manifolds, the tensor fields φ, h ($= (1/2)ℒ_{ξ}φ$), A ( = -∇ξ) fulfill a certain system of differential equations. It is proved that the leaves of the canonical foliation of an almost cosymplectic (κ,μ,ν)-space with κ<0 are locally flat Kählerian manifolds. A local characterization of such manifolds is established up to a 𝓓-homothetic transformation of the almost cosymplectic structures.