The Universidad Complutense de Madrid (UCM) Survey is a long-term project aiming at finding and analysing star-forming galaxies detected by their H$alpha$ emission in Schmidt objective-prism plates. The instrumental set-up limits the volume of the Universe surveyed to a redshift $zlesssim0.045$. So far we have discovered several hundred emission-line galaxies (ELGs) undergoing star formation at a wide range of levels. Analyzing a complete sample of ELGs from the UCM survey we have computed the H$alpha$ luminosity function for the star-forming galaxies in the surveyed volume of the Universe. A Schechter function provides a good fit to the H$alpha$ luminosity function with the following parameters: $alpha = -1.3pm0.2$; $L^*({ m H}alpha) = 10^{42.15pm0.08} $erg$ $s$^{-1}$ and $phi^*=10^{-3.2pm0.2} $Mpc$^{-3}$ for $H_0 = 50 $km$ $s$^{-1} $Mpc$^{-1}$. Integrating over the full range of luminosities, we obtain an H$alpha$ luminosity density of $10^{39.1pm0.2} $erg$ $s$^{-1} $Mpc$^{-3}$. Using the H$alpha$ emission as a star formation rate (SFR) estimator, this translates into a SFR density for the Local Universe of $0.013^{+0.007}_{-0.005} M_{odot} $yr$^{-1} $Mpc$^{-3}$ in star-forming galaxies with $EW($H$alpha+$[NII]$)>10$AA and $zlesssim0.045$, for a Scalo Initial Mass Function. This is the first observational determination of this quantity, which will provide a direct test of current galaxy formation and evolution models.