The energy spectrum of cosmic-ray antiprotons (p's) has been measured by BESS successively in 1993, 1995, 1997 and 1998. In total, 848 (p) over bar 's were clearly identified in energy range 0.18-4.20 GeV. From these successive measurements of the (p) over bar spectrum at various solar activity, we discuss about the effect of the solar modulation and the origin of cosmic-ray (p) over bar 's. The (p) over bar /p ratios showed no distinctive year-to-year variation during the positive Sun's polarity phase. (C) 2001 Elsevier Science B.V. All rights reserved.