  We calculate the full ${\cal O}(\alpha_{ew})$ electroweak corrections to the
Higgs pair production process $e^+ e^- \to H H Z$ at an electron-positron
linear collider in the standard model, and analyze the dependence of the Born
cross section and the corrected cross section on the Higgs boson mass $m_H$ and
the c.m. energy $\sqrt{s}$. To see the origin of some of the large corrections
clearly, we calculate the QED and genuine weak corrections separately. The
numerical results show that the corrections significantly suppress or enhance
the Born cross section, depending on the values of $m_H$ and $\sqrt{s}$. For
the c.m. energy $\sqrt{s} = 500 GeV$, which is the most favorable colliding
energy for $H H Z$ production with intermediate Higgs boson mass, the relative
correction decreases from -5.3% to -11.5% as $m_H$ increases from 100 to 150
GeV. For the range of the c.m. energy where the cross section is relatively
large, the genuine weak relative correction is small, less than 5%.
