To provide a heat development processor for a heat developable photosensitive material which reduces density unevenness in PS plate printing and has superior size stability.
This heat development processor carries the heat developable photosensitive material having been exposed to an image and develops it by heating; and the heat developable photosensitive material contains a compound which releases a substance having development acceleration effect as the heat development temperature rises and the heat development is carried out at such a conveyance speed that the relation between a gamma value variation quantity and a conveying speed variation quantity is represented by an expression (1) Δγ/Δs≤0.2, where Δγ is the gamma variation quantity and Δs is the conveying speed variation quantity (mm/sec).