An imaging apparatus for diagnosis comprising a probe comprising a sheath for accommodating an imaging core emitting a signal toward the biological tissues and detecting a reflected signal thereof and whose distal end has a guidewire lumen for guiding the imaging core to the biological tissues, and a guidewire, passing through the inside of the guidewire lumen, are used so as to move and rotate the imaging core along the sheath, a cross-sectional image generation means configured to generate a cross-sectional image at each axial position of the movement, based on data obtained via the imaging core by the movement and rotation of the imaging core inside the sheath; a detection means configured to detect a direction in which the guidewire is present in each of the cross-sectional images; a rotation means configured to rotate a target cross-sectional image detected by the detection means in accordance with an angular difference between the direction in which the guidewire is present and a pre-set direction in the target cross-sectional image, for each of the cross-sectional images; and a three-dimensional image generation means configured to generate a three-dimensional image along the movement direction of each of the cross-sectional images which are previously rotated by the rotation means; characterized in that the three-dimensional image generation means is configured to splitt the three-dimensional image along a guidewire image and unfold it to generate a two-dimensional image which includes a segment representing the guidewire in the three-dimensional image on each of an upper side and a lower side of the two-dimensional image. a probe comprising a sheath for accommodating an imaging core emitting a signal toward the biological tissues and detecting a reflected signal thereof and whose distal end has a guidewire lumen for guiding the imaging core to the biological tissues, and a guidewire, passing through the inside of the guidewire lumen, are used so as to move and rotate the imaging core along the sheath, a cross-sectional image generation means configured to generate a cross-sectional image at each axial position of the movement, based on data obtained via the imaging core by the movement and rotation of the imaging core inside the sheath; a detection means configured to detect a direction in which the guidewire is present in each of the cross-sectional images; a rotation means configured to rotate a target cross-sectional image detected by the detection means in accordance with an angular difference between the direction in which the guidewire is present and a pre-set direction in the target cross-sectional image, for each of the cross-sectional images; and a three-dimensional image generation means configured to generate a three-dimensional image along the movement direction of each of the cross-sectional images which are previously rotated by the rotation means; characterized in that the three-dimensional image generation means is configured to splitt the three-dimensional image along a guidewire image and unfold it to generate a two-dimensional image which includes a segment representing the guidewire in the three-dimensional image on each of an upper side and a lower side of the two-dimensional image.