The existence of the ground state of the so-called semi-relativistic Pauli-Fierz model is proven. Let A be a quantized radiation field and H f,m the free field Hamiltonians which is the second quantization of |k| 2 + m 2 . It has been established so far that the semi-relativistic Pauli-Fierz modelhas the unique ground state for (m, M ) ∈ {(0, ∞) × [0, ∞)} ∪ {[0, ∞) × (0, ∞)}. In this paper the existence of the ground state of H SRPF with (m, M ) ∈ [0, ∞) × [0, ∞) is shown. We emphasize that our results include a singular case (m, M ) = (0, 0), i.e., the existence of the ground state of the Hamiltonian of the form: |− i∇ ⊗ 1l − A| + V ⊗ 1l + 1l ⊗ H f,0 is established.