a scanner configured to apply an OCT scan with a measurement light to an object using an optical scanner;

a controller circuit configured to control the scanner to perform at least one first scan that scans a first cross section of the object in a first scan direction and at least one second scan that scans a second cross section of the object in a second scan direction opposite to the first scan direction;

a phase information generator circuit configured to generate at least one piece of first phase information based on at least one piece of first acquisition data acquired by the at least one first scan and at least one piece of second phase information based on at least one piece of second acquisition data acquired by the at least one second scan; and

a phase information processor circuit configured to generate composite phase information based on the at least one piece of first phase information and the at least one piece of second phase information, wherein

the scanner includes a reflecting mirror configured to rotate about an axis,

the measurement light is reflected at a position off the axis of the reflecting mirror, and

the phase information processor circuit is further configured to eliminate an error in the generated composite phase information caused by the measurement light being reflected at the position off the axis of the reflecting mirror.