An OCT data processing device (40, 1) configured to process OCT data of a tissue of a subject's eye acquired by an OCT device, wherein the OCT device comprises: an OCT light source; a branching optical element configured to divide light emitted from the OCT light source into measurement light and reference light; an irradiation optical system configured to irradiate the measurement light divided by the branching optical element onto the tissue; a multiplexing optical element configured to combine the measurement light reflected by the tissue and the reference light divided by the branching optical element and cause the measurement light and the reference light to interfere with each other; and a photodetector configured to detect an interference signal by receiving interference light generated by the multiplexing optical element, and a processor (41, 31) of the OCT data processing device is configured to: acquire three-dimensional OCT data, the three-dimensional OCT data being three-dimensional OCT data obtained by irradiating the measurement light on a two-dimensional measurement region, the two-dimensional measurement region extending in a direction intersecting an optical axis of the measurement light; set a line pattern after acquiring the three-dimensional OCT data, from among a plurality of types of line pattern, with respect to the two-dimensional measurement region for which the three-dimensional OCT data is obtained, at least one of an arrangement, a number, or a shape of one or more lines being different for the plurality of types of line pattern; and extract, from the three-dimensional OCT data, a two-dimensional tomographic image (73A, 73B) of a cross section intersecting each of the one or more lines of the set line pattern, wherein the plurality of types of line pattern are stored in a memory, and the processor is configured to set the line pattern by selecting, from among the plurality of types of line pattern, one or more line patterns. the OCT device comprises: an OCT light source; a branching optical element configured to divide light emitted from the OCT light source into measurement light and reference light; an irradiation optical system configured to irradiate the measurement light divided by the branching optical element onto the tissue; a multiplexing optical element configured to combine the measurement light reflected by the tissue and the reference light divided by the branching optical element and cause the measurement light and the reference light to interfere with each other; and a photodetector configured to detect an interference signal by receiving interference light generated by the multiplexing optical element, and an OCT light source; a branching optical element configured to divide light emitted from the OCT light source into measurement light and reference light; an irradiation optical system configured to irradiate the measurement light divided by the branching optical element onto the tissue; a multiplexing optical element configured to combine the measurement light reflected by the tissue and the reference light divided by the branching optical element and cause the measurement light and the reference light to interfere with each other; and a photodetector configured to detect an interference signal by receiving interference light generated by the multiplexing optical element, and a processor (41, 31) of the OCT data processing device is configured to: acquire three-dimensional OCT data, the three-dimensional OCT data being three-dimensional OCT data obtained by irradiating the measurement light on a two-dimensional measurement region, the two-dimensional measurement region extending in a direction intersecting an optical axis of the measurement light; set a line pattern after acquiring the three-dimensional OCT data, from among a plurality of types of line pattern, with respect to the two-dimensional measurement region for which the three-dimensional OCT data is obtained, at least one of an arrangement, a number, or a shape of one or more lines being different for the plurality of types of line pattern; and extract, from the three-dimensional OCT data, a two-dimensional tomographic image (73A, 73B) of a cross section intersecting each of the one or more lines of the set line pattern, wherein acquire three-dimensional OCT data, the three-dimensional OCT data being three-dimensional OCT data obtained by irradiating the measurement light on a two-dimensional measurement region, the two-dimensional measurement region extending in a direction intersecting an optical axis of the measurement light; set a line pattern after acquiring the three-dimensional OCT data, from among a plurality of types of line pattern, with respect to the two-dimensional measurement region for which the three-dimensional OCT data is obtained, at least one of an arrangement, a number, or a shape of one or more lines being different for the plurality of types of line pattern; and extract, from the three-dimensional OCT data, a two-dimensional tomographic image (73A, 73B) of a cross section intersecting each of the one or more lines of the set line pattern, wherein the plurality of types of line pattern are stored in a memory, and the processor is configured to set the line pattern by selecting, from among the plurality of types of line pattern, one or more line patterns.