  We used three indicators of massive star formation: $H_{\alpha}$, FIR and
non-thermal radio luminosities, to compare estimations of Star Formation Rate
(SFR) for the sample of 34 spiral galaxies. To adjust SFR values, obtained from
different indicators, we considered the slope $\alpha$ and/or upper mass limit
$M_{up}$ of Initial Mass Function (IMF) as free parameters. The best agreement
between these indicators reaches for $M_{up} \approx 60 - 100 ~M_{\odot}$ and
$\alpha \approx -3.1 $ in the high mass end of IMF ($M > 10 ~M_{\odot}$).
Parallel with SFR we also estimated FIR excess $X_{FIR}$ defined as a fraction
of the observed FIR which is not related to young massive stars directly.
$X_{FIR}$ is found to be well correlated with types of spiral galaxies and
their colors (B-V): the redder a galaxy the higher is its FIR excess. We
conclude that for any parameters of IMF the observed FIR flux of early type
spiral galaxies needs the additional source of energy but the massive star
radiation.
