The secondaries of the massive binary systems can be found as runaway stars after being ejected due to the supernova (SN) of the more massive component. We search for such stars inside the supernova remnants (SNRs), where a recent SN is guaranteed to have happened, and the runaway star is expected to be nearby. In this paper, we present the massive runaway star HD 254577 as the pre-supernova binary companion to the progenitor of the supernova remnant IC 443 and the neutron star (NS) CXOU J61705.3+222127. We performed spectroscopic observations of the runaway star and specified its atmospheric parameters. We also used archival spectroscopic data on neighboring stars. Together with the precise Gaia DR3 astrometry and photometry, we identified the possible birth origin of the runaway star, and by isochrone fitting, we determined the progenitor mass. From the Gaia DR3 proper motions, we specified the possible explosion sites and calculated the neutron star (NS) velocity. HD 254577 is a hot and evolved star with an effective temperature of 24000+/-1000K (B0.5II) and a surface gravity of log(g[cm/s^2^])=2.75+/-0.25. It is probably a single star with a peculiar 3-D velocity of 31.3^+1.2^_-0.9_km/s, lying at a heliocentric distance of 1701^+55^_-54_pc. The cometary tail of the NS implies that it is moving away from the same site as the runaway star. From the flight trajectories, we calculated that the NS has typical pulsar velocities such as 254-539km/s at a distance of 1.7kpc for 10-20kyr ages. Together with the blue-only shifted interstellar medium lines on its spectrum, HD 254577 must be the pre-supernova binary companion to the progenitor of IC 443. By identifying the pre-supernova companion and the possible parent cluster, we showed that the progenitor zero-age main sequence mass is high: 31-64M_{sun}_, favoring the jet scenario previously proposed. The SNR distance is precisely determined as 1701^+55^_-54_pc. We also discuss the expansion dynamics of the SNR due to the highly off-centered explosion site. The pre-SN binary parameters that we calculated might not favor a strongly interacting binary.