We study the superconductivity in typical $d$-band elemental superconductors V and Nb with the recently developed non-empirical computational scheme based on the density functional theory for superconductors. The effect of ferromagnetic fluctuation (paramagnon) on the superconducting transition temperature ($T_{rm c}$), which in principle suppress the $s$-wave superconducting pairing, is quantified without any empirical parameter. We show that the strong paramagnon effect cancels the $T_{rm c}$-enhancing effects of the phonon-mediated pairing and dynamical screened Coulomb interaction.
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