We study the detectability of the stoponium in the di-Higgs decay mode at the photon-photon collider option of the International $e^+e^-$ Linear Collider (ILC), whose center-of-mass energy is planned to reach $sim 1$ TeV. We find that $5sigma$ detection of the di-Higgs decay mode is possible with the integrated electron-beam luminosity of $1 {rm ab}^{-1}$ if the signal cross section, $sigma(gamma gamma rightarrow sigma_{tilde{t}_1} rightarrow hh)$, of ${cal O}(0.1)$ fb is realized for the stoponium mass smaller than $sim$ 800 GeV at 1 TeV ILC. Such a value of the cross section can be realized in the minimal supersymmetric standard model (MSSM) with relatively large trilinear stop-stop-Higgs coupling constant. Implication of the stoponium cross section measurement for the MSSM stop sector is also discussed.
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