To obtain an image by using an image recording medium which has high thermal sensitivity, permits execution of recording by a laser of a low output in such a degree as not to cause ablation even in the case of utilizing an image recording system of a heat mode using the laser, necessitates no separate image receiving sheet and is excellent in shelf stability.

An image is formed by using an image recording medium containing a compound wherein the combination with phosphorus in a phosphoric acid derivative is cut off by the effect of heat or an acid and a change occurs in absorption between 360 nm and 900 nm by the combination cleavage in the derivative or a reaction subsequent thereto. Moreover, the image recording medium contains a compound producing the acid by the effect of light or heat. Besides, it contains an infrared ray absorbing compound.