An image processing apparatus comprising: a storage unit to store moving-image data including a plurality of frames captured by an image-capturing device communicable with the image processing apparatus, time-series data of an inclination angle of the image-capturing device with reference to a reference direction, and time-series data of angular velocities generated around three axes of an angular velocity sensor of the image-capturing device; and a correction unit to, based on the time-series data of the angular velocities, rotate an image of each of the plurality of frames of the moving-image data to reduce a rotational distortion around the reference direction; and an output unit to output image data of the rotated image of each of the plurality of frames to an external device communicable with the image processing apparatus, characterized in that the image processing apparatus further comprises a camera front calculation unit to calculate a first front direction of the image-capturing device at a first time based on a value of the time-series data of the inclination angle at the first time, and after obtaining the first front direction, to calculate time-series values of the front direction of the image-capturing device over a plurality of times corresponding to the plurality of frames based on the time-series data of the angular velocities, wherein the front direction is the direction of an optical axis of the image-capturing device; a correction angle calculation unit to calculate a correction angle for the rotation correction from the time-series values of the front direction of the image-capturing device in a predetermined frame among the plurality of frames, based on the time-series data of the inclination angle, wherein the correction unit rotates the image based on the calculated correction angle. a storage unit to store moving-image data including a plurality of frames captured by an image-capturing device communicable with the image processing apparatus, time-series data of an inclination angle of the image-capturing device with reference to a reference direction, and time-series data of angular velocities generated around three axes of an angular velocity sensor of the image-capturing device; and a correction unit to, based on the time-series data of the angular velocities, rotate an image of each of the plurality of frames of the moving-image data to reduce a rotational distortion around the reference direction; and an output unit to output image data of the rotated image of each of the plurality of frames to an external device communicable with the image processing apparatus, characterized in that the image processing apparatus further comprises a camera front calculation unit to calculate a first front direction of the image-capturing device at a first time based on a value of the time-series data of the inclination angle at the first time, and after obtaining the first front direction, to calculate time-series values of the front direction of the image-capturing device over a plurality of times corresponding to the plurality of frames based on the time-series data of the angular velocities, wherein the front direction is the direction of an optical axis of the image-capturing device; a correction angle calculation unit to calculate a correction angle for the rotation correction from the time-series values of the front direction of the image-capturing device in a predetermined frame among the plurality of frames, based on the time-series data of the inclination angle, wherein the correction unit rotates the image based on the calculated correction angle.