To appropriately execute a preliminary operation for OCT measurement of an eye to be examined.SOLUTION: A change in an optical path length difference is executed so as to adjust an optical path length difference between arms to dispose an image of an eye to be examined at a reference position based on data acquired in iterative OCT scanning, and dispose it at a new reference position. Whether or not to execute the change in an optical path length difference is determined based on data acquired while a preliminary operation is executed. This determination includes determination on whether or not a distance between an image of a retina surface and a frame upper end is a threshold or less, and the change in an optical path length difference is executed when the distance is determined to be a threshold or less. The change in an optical path length difference is executed so that a new reference position is set more on the frame upper end side than the aforesaid reference position.SELECTED DRAWING: Figure 3【課題】被検眼のＯＣＴ計測のための予備動作を好適に実行する。【解決手段】反復的ＯＣＴ走査で得られるデータに基づき被検眼の像を基準位置に配置するようアーム間の光路長差を調整し、かつ新たな基準位置に配置するよう光路長差変更を行う。予備動作実行中に得たデータに基づき光路長差変更を行うか判定する。この判定は、網膜表面の画像とフレーム上端との距離が閾値以下かの判定を含み、この距離が閾値以下と判定されたときに光路長差変更を行う。この光路長差変更は、基準位置よりもフレームの上端側に新たな基準位置を設定するように行われる。【選択図】図３
