PURPOSE: To provide the holding device for the substrate for mask plotting which precisely holds the substrate and prevents a plotted pattern from being distorted.

CONSTITUTION: The holding device is provided with holding mechanisms 4, which hold both side parts of the substrate 17, on both the widthdirectional sides of a device body 1, and each holding mechanism 4 is equipped with a movable plate 5 which elastically comes into contact with and leaves the top surface of the main body 1 through a spring body 7 in a parallel state, 1st projections which are provided at both the length-directional end parts on the top surface of the movable plate 5 and abuts on the reverse surface of the side parts of the substrate supplied to the top surface side of the movable plate 5, a reference plate 15 which is arranged on the main body 1 opposite the top surface of the movable plate 5, and 2nd projections which are provided on the reverse surface of the reference plate 15 more outside the 1st projections in the width direction of the main body 1 and abut on the top surface of the substrate 17 pushed up by the 1st projections of the movable plate 5.