An image recording apparatus comprising: a transport mechanism for transporting an elongated strip-shaped recording medium in a longitudinal direction thereof along a predetermined transport path; at least one recording head for recording an image on a surface of the recording medium in a recording position on said transport path; an upstream detector (30a, 30b, 30c, 30d) for detecting a widthwise position of the recording medium in a position upstream of said recording position on said transport path; a downstream detector (30b, 30c, 30d, 30e) for detecting the widthwise position of the recording medium in a position downstream of said recording position on said transport path; and a calculation part for calculating the widthwise position of the recording medium in said recording position, based on detection results from said upstream detector and said downstream detector; wherein said at least one recording head covers the full width of the recording medium, and said at least one recording head includes a plurality of recording heads (21, 22, 23, 24); said recording heads include a first recording head for recording an image on the surface of the recording medium in a first recording position on said transport path, and a second recording head (22 or 23 or 24) for recording an image on the surface of the recording medium in a second recording position downstream of said first recording position on said transport path; characterised by the fact that said upstream detector and said downstream detector are provided for each of said first and second recording positions, said calculation part calculates a relative widthwise position of the recording medium in said second recording position with reference to the widthwise position of the recording medium in said first recording position, said calculation part makes a comparison between results of detection of the same portion of the recording medium which are obtained from said upstream detectors (30a, 30b, 30c, 30d) for said first and second recording positions, and makes a comparison between results of detection of the same portion of the recording medium which are obtained from said downstream detectors (30b, 30c, 30d, 30e) for said first and second recording positions, to thereby calculate said relative widthwise position, said results of detection from said upstream detectors for said first and second recording positions are obtained at different times by the amount of transport time of the recording medium, said results of detection from said downstream detectors for said first and second recording positions are obtained at different times by the amount of transport time of the recording medium. a transport mechanism for transporting an elongated strip-shaped recording medium in a longitudinal direction thereof along a predetermined transport path; at least one recording head for recording an image on a surface of the recording medium in a recording position on said transport path; an upstream detector (30a, 30b, 30c, 30d) for detecting a widthwise position of the recording medium in a position upstream of said recording position on said transport path; a downstream detector (30b, 30c, 30d, 30e) for detecting the widthwise position of the recording medium in a position downstream of said recording position on said transport path; and a calculation part for calculating the widthwise position of the recording medium in said recording position, based on detection results from said upstream detector and said downstream detector; wherein said at least one recording head covers the full width of the recording medium, and said at least one recording head includes a plurality of recording heads (21, 22, 23, 24); said recording heads include a first recording head for recording an image on the surface of the recording medium in a first recording position on said transport path, and a second recording head (22 or 23 or 24) for recording an image on the surface of the recording medium in a second recording position downstream of said first recording position on said transport path; characterised by the fact that said upstream detector and said downstream detector are provided for each of said first and second recording positions, said calculation part calculates a relative widthwise position of the recording medium in said second recording position with reference to the widthwise position of the recording medium in said first recording position, said calculation part makes a comparison between results of detection of the same portion of the recording medium which are obtained from said upstream detectors (30a, 30b, 30c, 30d) for said first and second recording positions, and makes a comparison between results of detection of the same portion of the recording medium which are obtained from said downstream detectors (30b, 30c, 30d, 30e) for said first and second recording positions, to thereby calculate said relative widthwise position, said results of detection from said upstream detectors for said first and second recording positions are obtained at different times by the amount of transport time of the recording medium, said results of detection from said downstream detectors for said first and second recording positions are obtained at different times by the amount of transport time of the recording medium.