A recording device comprising: an image/audio recording unit for adding a time code to moving image data obtained by imaging a state in which a person who is writing a description and explaining while writing the description in a description portion, such that the person and the description portion are imaged, and audio data corresponding to the moving image data to record the data in a recording unit; and an index-image generation unit for processing the moving image data, determining a written portion in the description portion, generating index image data for displaying, as an index description, groups of pixels having been determined as being the written portion, and recording the index image data in a recording unit, wherein the index-image generation unit is configured to extract a difference value between a current frame image and a reference frame image for each pixel, to grasp groups of a series of pixels having a difference value equal to or more than a threshold value, and to determine whether each group has the written portion or not, and the index-image generation unit is configured to determine whether each of the groups has the written portion or not by using a shape evaluation value (α), an extraction time evaluation value (β), and a stationary time evaluation value (γ), wherein the index-image generation unit is configured to: determine the shape evaluation value (α) on a basis of a relationship between aspect ratios of a minimum square containing the group and a maximum square contained in the group, obtain the extraction time evaluation value (β) on a basis of a value of a difference from the reference frame image, in a pixel included in the group, over a current frame and a plurality of frames prior to the current frame, and obtain the stationary time evaluation value (γ) on a basis of a value of a difference from a frame image of a preceding frame, in a pixel included in the group, over a current frame and a plurality of frames prior to the current frame, wherein, to the index image data, a value of the time code corresponding to description time is added as a timestamp, in association with pixels constituting the index description. an image/audio recording unit for adding a time code to moving image data obtained by imaging a state in which a person who is writing a description and explaining while writing the description in a description portion, such that the person and the description portion are imaged, and audio data corresponding to the moving image data to record the data in a recording unit; and an index-image generation unit for processing the moving image data, determining a written portion in the description portion, generating index image data for displaying, as an index description, groups of pixels having been determined as being the written portion, and recording the index image data in a recording unit, wherein the index-image generation unit is configured to extract a difference value between a current frame image and a reference frame image for each pixel, to grasp groups of a series of pixels having a difference value equal to or more than a threshold value, and to determine whether each group has the written portion or not, and the index-image generation unit is configured to determine whether each of the groups has the written portion or not by using a shape evaluation value (α), an extraction time evaluation value (β), and a stationary time evaluation value (γ), wherein the index-image generation unit is configured to: determine the shape evaluation value (α) on a basis of a relationship between aspect ratios of a minimum square containing the group and a maximum square contained in the group, obtain the extraction time evaluation value (β) on a basis of a value of a difference from the reference frame image, in a pixel included in the group, over a current frame and a plurality of frames prior to the current frame, and obtain the stationary time evaluation value (γ) on a basis of a value of a difference from a frame image of a preceding frame, in a pixel included in the group, over a current frame and a plurality of frames prior to the current frame, determine the shape evaluation value (α) on a basis of a relationship between aspect ratios of a minimum square containing the group and a maximum square contained in the group, obtain the extraction time evaluation value (β) on a basis of a value of a difference from the reference frame image, in a pixel included in the group, over a current frame and a plurality of frames prior to the current frame, and obtain the stationary time evaluation value (γ) on a basis of a value of a difference from a frame image of a preceding frame, in a pixel included in the group, over a current frame and a plurality of frames prior to the current frame, wherein, to the index image data, a value of the time code corresponding to description time is added as a timestamp, in association with pixels constituting the index description.