The Hamiltonian h of the system of two quantum particles moving on a 3-dimensional lattice interacting via some attractive potential is considered. Conditions for the existence of eigenvalues of the two-particle Schr ödinger operator h µ (k), k ∈ T 3 , µ ∈ R, associated to the Hamiltonian h, are studied depending on the energy of the particle interaction µ ∈ R and total quasi-momentum k ∈ T 3 (T 3 -three-dimensional torus). KEYWORDS two-particle Hamiltonian, invariant subspace, unitary equivalent operator, virtual level, multiplicity of virtual level, eigenvalue.