The relation between the solar wind speed (V) observed at the earth's distance and the latitudinal angular distance of the earth (&lgr;) from the magnetic angular distance of the earth &lgr;) from the magnetic neutral line on the so-called ''source surface'' of the sun, which is determined from the spherical harmonic analysis of the line-of-sight component of the photospheric magnetic field [Hoeksema et al., 1982>, is examiend. It is shown that the solar wind speed V increases as ‖&lgr;‖ increased amd that V does not depend on the heliographic latitude of the earth. This relation may be represented by V(km/s)=408+473sin2&lgr; during the period between May 1976 and August 1977. The presence of such a latitudinal gradient of V indicates that some of the time variations of V observed at the earth and caused by the spatial variations of V with respect to &lgr;.