Based on high-resolution observations (R=60000 and 75000), we have studied the optical spectral variability of the star BD+48 1220, identified with the IR-source IRAS 05040+4820. We have measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths from 4500 to 6760{AA}, as well as the corresponding radial velocities. We use model atmospheres to determine the effective temperature Teff=7900K, surface gravity log g=0.0, microturbulence velocity xi_t_=6.0, and the abundances for 16 elements. The star's metallicity differs little from the solar value: [Fe/H]=-0.10dex. The main peculiarity of the chemical composition of the star is a large He-excess, derived from the HeI 5876{AA} absorption, [He/H]=+1.04, and the equally large O-excess, [O/Fe]=+0.72dex. The C-excess is small, [C/Fe]=+0.09dex, and the ratio [C/O]<=1. We obtained a revised relation for the light-metal abundances: [Na/Fe]=+0.87 with [Mg/Fe]=-0.31. The barium abundance is low, [Ba/Fe]=-0.84. The radial velocity of the star measured from photospheric absorption lines over three years of observations varies in the interval V_{sun}_=-(7-15)km/s. Time variable differential line shifts have been revealed. The entire set of available data (the luminosity Mv~-5mag, velocity V_lsr_~-20km/s, metallicity [Fe/H]=-0.10, and peculiarities of the optical spectrum and chemical composition) confirms the status of BD+48 1220 as a post-AGB star with He- and O-excesses belonging to the Galactic disk.