To provide substitution liquid for the print head of an active light beam curing ink jet printer and for preventing clogging of a nozzle, and to provide a substitution method for liquid in the print head.

The substitution liquid for the print head of an active light beam curing ink jet printer which is used when the print head of the active light beam curing ink jet printer is filled with ink or when the print head filled with ink is refilled with different ink satisfies following conditions (1) and (2). (1) The print head is at least filled once with the substitution liquid or the replacing liquid circulates through the print head before the print head is filled with ink. (2) The replacing liquid contains such a solvent as the solubility below 25°C for optical initiator contained in ink filling the print head anew becomes higher than the solubility below 25°C of the ink filling the print head anew.