In the minimal supersymmetric standard madel, it is shown that a radiative correction of the top and stop loops gives a finite, but non-negligible contribution to Higgs scalar masses if m, ' 150-250 GeV. The upper limit to the lightest-scalar mass becomes 70-190 GeV in the range of heavy top quark. 1 The mechanism of electroweak symmetry breaking is one of the most important issues in the present particle physics_ In the standard electroweak model a funda mental Higgs doublet is introduceq to cause the spontaneous symmetry breaking. Supersymmetry (SUSY), eliminating all quadratic divergences, may provide a better theoretical basis to describe a fundamental Higgs boson with a relatively small mass to a high energy cutoff scale, say the Planck scale for example. I) In the minimal SUSY extension of the standard electroweak model the Higgs sector consists of two chiral superfields of Higgs doublets (/JHl and (/JH2 with opposite hypercharges. They are required to give masses for all quarks and leptons and to guarantee the ~bsence of the gauge anomaly. Five physical Higgs bosons among them survive the gauge symmetry breaking, namely, there appear two neutral scalars rpa and rpb, a neutral pseudoscalar X and a pair of charged scalars x± as physical particles. It has been, furthermore, shown by many authors 2 ) that there is at least one neutral scalar boson lighter than ZO(m<p< mzo) in the minimal SUSY model. This has strongly motivated many recent analyses of Higgs boson production at LEP energies. 3 ) In this paper, however, we stress that a radiative correctiQn gives a significant contribution to the Higgs mass term if the top quark is 8uficiently heavy as mt ~150-250 GeV. Therefore, the presence of the Higgs scalar lighter than mzo is not an inevitable prediction of the minimal SUSY standard model. Let us discuss the Higgs sedor in the minimal SUSY model. With general soft-breaking terms 4 ) of SUSY the tree-level Higgs potential is given by