An OCT apparatus comprising: an OCT optical system that has a light splitter splitting light from an OCT light source to light traveling to a measurement light path and light traveling to a reference light path, and a detector detecting an interference signal of measurement light guided onto a fundus of a subject eye via the measurement light path and reference light from the reference light path; an image processor that is capable of processing a spectral interference signal output from the OCT optical system to acquire OCT data; and a light guiding optical system that is an optical system disposed on the measurement light path, that has an optical scanner deflecting the measurement light from the light splitter, that forms a pivot point, at which the measurement light turns based on motion of the optical scanner, in an anterior portion of the subject eye, and that guides the measurement light passed through the pivot point to the fundus, wherein the light guiding optical system is capable of switching to either an insertion state in which an angle-of-view switching optical system is inserted into the light guiding optical system or a retraction state in which the angle-of-view switching optical system is retracted from the light guiding optical system, a size of an angle of view indicating a scanning range of the measurement light on the fundus in the insertion state is different from a size of the angle of view in the retraction state, and the OCT optical system includes a compensation unit that compensates for an amount of change in a light path length of the measurement light path between the insertion state and the retraction state, characterized in that the compensation unit includes a light path branching portion that causes branching of at least a part of the reference light path of the OCT optical system, and forms a first branched light path having a first light path length corresponding to a light path length of the measurement light path in the retraction state and a second branched light path having a second light path length corresponding to a light path length of the measurement light path in the insertion state. an OCT optical system that has a light splitter splitting light from an OCT light source to light traveling to a measurement light path and light traveling to a reference light path, and a detector detecting an interference signal of measurement light guided onto a fundus of a subject eye via the measurement light path and reference light from the reference light path; an image processor that is capable of processing a spectral interference signal output from the OCT optical system to acquire OCT data; and a light guiding optical system that is an optical system disposed on the measurement light path, that has an optical scanner deflecting the measurement light from the light splitter, that forms a pivot point, at which the measurement light turns based on motion of the optical scanner, in an anterior portion of the subject eye, and that guides the measurement light passed through the pivot point to the fundus, wherein the light guiding optical system is capable of switching to either an insertion state in which an angle-of-view switching optical system is inserted into the light guiding optical system or a retraction state in which the angle-of-view switching optical system is retracted from the light guiding optical system, a size of an angle of view indicating a scanning range of the measurement light on the fundus in the insertion state is different from a size of the angle of view in the retraction state, and the OCT optical system includes a compensation unit that compensates for an amount of change in a light path length of the measurement light path between the insertion state and the retraction state, characterized in that the compensation unit includes a light path branching portion that causes branching of at least a part of the reference light path of the OCT optical system, and forms a first branched light path having a first light path length corresponding to a light path length of the measurement light path in the retraction state and a second branched light path having a second light path length corresponding to a light path length of the measurement light path in the insertion state.