To form a dark tone image through high sensitivity image recording by employing a thermal recording material having a layer for forming an image utilizing a thermally reductive metal compound, e.g. organic silver salt.

A thermal recording material A having a thermal image forming layer containing a thermally reductive metal compound, e.g. organic silver salt, is employed. A thermal recorder 10 exposes the thermal recording material A imagewise with an optical beam L for thermal recording (heat mode laser). The recorder for recording an image by heating the thermal recording material A imagewise comprises an optical system 12 for irradiating the material A with the optical beam L, means 14 for subscan carrying the material A while holding at a recording position X, means 36 for preheating the material A on which an image is recorded, and means 38 for postheating the material A recorded with an image.