A three-dimensional image forming device for forming a continuous three-dimensional image on the basis of images of an inner face of a tubular structure to be observed, comprising: an imaging unit having an objective lens and having an optical axis extending in an axial direction of the tubular structure, for obtaining a plurality of frame images while moving in the tubular structure under specified lighting condition; a test line setting unit for setting on each frame image a circular test line with a center corresponding to the optical axis of the imaging unit; a luminance information extracting unit for extracting luminance information of pixels corresponding to the circular test line of each frame image of the inner face of the tubular structure acquired by the imaging unit; a distance information calculating unit for calculating relative distances in a depth direction between points on the inner face of the tubular structure and the objective lens on the basis of the luminance information extracted by the luminance information extracting unit; a three-dimensional image forming unit for forming a three-dimensional image of the inner face of the tubular structure by arraying the pixels corresponding to the circular test line of each frame image of the inner face of the tubular structure while reflecting the relative distances to the arraying, and combining the arrayed pixels for a plurality of frame images; characterized by further comprising a motion detecting device including an axial direction sensor configured for detecting a motion amount of the imaging unit in the axial direction from a reference position in the axial direction and a circumferential direction sensor configured for detecting a rotation motion amount of the imaging unit in a circumferential direction of the imaging unit from a reference position in the circumferential direction, wherein the three-dimensional image forming unit corrects the image composed by the arrayed pixels in the circumferential direction and/or axial direction on the basis of the detected motion amounts from the motion detecting device; wherein, in order to correct the image in the circumferential direction, the three-dimensional image forming unit shifts the pixels on the circular test line of each frame image in the circumferential direction based on the motion amount of the imaging unit in the circumferential direction, and in order to correct the image in the axial direction, the three-dimensional image forming unit interpolates two consecutive arrayed pixels acquired on the circular test lines when the motion amount in the axial direction is large, creating interpolated pixel array data which are disposed between those two arrayed pixels, or employs one piece of arrayed pixels when there are a plurality of pieces of arrayed pixels acquired at nearly same position in the inner face of the tubular body. an imaging unit having an objective lens and having an optical axis extending in an axial direction of the tubular structure, for obtaining a plurality of frame images while moving in the tubular structure under specified lighting condition; a test line setting unit for setting on each frame image a circular test line with a center corresponding to the optical axis of the imaging unit; a luminance information extracting unit for extracting luminance information of pixels corresponding to the circular test line of each frame image of the inner face of the tubular structure acquired by the imaging unit; a distance information calculating unit for calculating relative distances in a depth direction between points on the inner face of the tubular structure and the objective lens on the basis of the luminance information extracted by the luminance information extracting unit; a three-dimensional image forming unit for forming a three-dimensional image of the inner face of the tubular structure by arraying the pixels corresponding to the circular test line of each frame image of the inner face of the tubular structure while reflecting the relative distances to the arraying, and combining the arrayed pixels for a plurality of frame images; characterized by further comprising a motion detecting device including an axial direction sensor configured for detecting a motion amount of the imaging unit in the axial direction from a reference position in the axial direction and a circumferential direction sensor configured for detecting a rotation motion amount of the imaging unit in a circumferential direction of the imaging unit from a reference position in the circumferential direction, wherein the three-dimensional image forming unit corrects the image composed by the arrayed pixels in the circumferential direction and/or axial direction on the basis of the detected motion amounts from the motion detecting device; wherein, in order to correct the image in the circumferential direction, the three-dimensional image forming unit shifts the pixels on the circular test line of each frame image in the circumferential direction based on the motion amount of the imaging unit in the circumferential direction, and in order to correct the image in the axial direction, the three-dimensional image forming unit interpolates two consecutive arrayed pixels acquired on the circular test lines when the motion amount in the axial direction is large, creating interpolated pixel array data which are disposed between those two arrayed pixels, or employs one piece of arrayed pixels when there are a plurality of pieces of arrayed pixels acquired at nearly same position in the inner face of the tubular body.