&lt; 269 [ GeV]{}, \[lightest\] which is considerably lower than that of the SM Higgs boson, 712 GeV. This condition comes from the constraints $|x_1^+|<8\pi$ and $|x_5^-|<8\pi$. Similar analysis has been done for $m_{\rm lightest}^{} = m_{H_5}^{},
m_{\tilde H_1^0}$ and $m_{\tilde H_1^{0'}}$ in order, and the same bound as in Eq.(\[lightest\]) is derived for each case. When $m_{\rm lightest}^{} \simeq 269$ GeV, all the masses are degenerate in mass ($m_{H_3}^{} = m_{H_5}^{} = m_{\tilde H_1^0} = m_{\tilde H_1^{0'}}$). The situation turns out to be quite similar to the situation of the two-Higgs-doublet model with the discrete symmetry, where the lightest of all Higgs masses are bounded at 410 GeV [@Kanemura:1993hm]. In the case of the GM model the number of the two-body states is greater than that in the two-Higgs-doublet model. (The neutral two body states are 14 channels in the two-Higgs-doublet model and 25 channels in the GM model.) Thereby we have obtained the stronger bounds than the two-Higgs-doublet model. Finally, when we take into account the $Zb\bar b$ results [@Haber:1999zh], the angle $\theta_H$ is more limited for smaller values of $m_{H_3}^{}$. Consequently, the combined upper bound on $m_{\rm lightest}^{}$ becomes lower than 269 GeV. Depending on what the 