We have studied the relationship between the solar-wind speed [V]\documentclass[12pt]{minimal}
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\begin{document}$[V]$\end{document} and the coronal magnetic-field properties (a flux-expansion factor [f\documentclass[12pt]{minimal}
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\begin{document}$f$\end{document}] and photospheric magnetic-field strength [BS\documentclass[12pt]{minimal}
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\begin{document}$B_{\mathrm{S}}$\end{document}]) at all latitudes using data of interplanetary scintillation and solar magnetic field obtained for 24 years from 1986 to 2009. Using a cross-correlation analyses, we verified that V\documentclass[12pt]{minimal}
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\begin{document}$V$\end{document} is inversely proportional to f\documentclass[12pt]{minimal}
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\begin{document}$f$\end{document} and found that V\documentclass[12pt]{minimal}
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\begin{document}$V$\end{document} tends to increase with BS\documentclass[12pt]{minimal}
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\begin{document}$B_{\mathrm{S}}$\end{document} if f\documentclass[12pt]{minimal}
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\begin{document}$f$\end{document} is the same. As a consequence, we find that V\documentclass[12pt]{minimal}
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\begin{document}$V$\end{document} has an extremely good linear correlation with BS/f\documentclass[12pt]{minimal}
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\begin{document}$B_{\mathrm{S}}/f$\end{document}. However, this linear relation of V\documentclass[12pt]{minimal}
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\begin{document}$V$\end{document} and BS/f\documentclass[12pt]{minimal}
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\begin{document}$B_{\mathrm{S}}/f$\end{document} cannot be used for predicting the solar-wind velocity without information on the solar-wind mass flux. We discuss why the inverse relation between V\documentclass[12pt]{minimal}
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\begin{document}$V$\end{document} and f\documentclass[12pt]{minimal}
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\begin{document}$f$\end{document} has been successfully used for solar-wind velocity prediction, even though it does not explicitly include the mass flux and magnetic-field strength, which are important physical parameters for solar-wind acceleration.
