To provide a platemaking method for a photosensitive planographic printing plate having excellent contamination prevention during printing and printing durability without damaging image characteristics (in particular, fog in a non-image part and stability of the sensitivity), and also to provide a method for forming an image.

The platemaking method for a photosensitive planographic printing plate is characterized in that: when the transport velocity of the photosensitive planographic printing plate material in a step of heating the plate material is controlled to 0.6 to 1.5 m/min and the temperature of the heat generating part in the heating step is controlled to 300 to 500°C, the space volume above the transport line of the photosensitive planographic printing plate material is expressed as A, and the space volume under the line is expressed as B, relational expression (1) defined by space volume ratio=space volume A/space volume B satisfies 1.0 to 20; and that when X mm is the width of the photosensitive planographic printing plate material in the heating step, the entire space volume in the heating step is smaller than expression (2)=(X (width)×1.1) mm×200 mm (depth)×200 mm (height).