PURPOSE: To enable stable delivery and high-speed deposition by incorporating a colorant and a specific naphthalene compound.

CONSTITUTION: A colorant, e.g. a direct, acid, basic, disperse, or vat dye, is mixed, in an amount of 0.2-30wt.% with 15-90wt.% naphthalene compound represented by the formula (wherein R is a group selected from alkyls, alkoxys, and hydroxyl and n is 1-3), 20-90wt.% wax or resin, and 0-10wt.% organic solvent having a b.p. of 150°C or higher to obtain a recording medium which is solid at ordinary temp and has a melting point of 36-200°C. A tank 1 containing this medium, a feed line 2, and a recording head 3 are heated with heating means 8 and 4 by a temp. controller 6 to a temp. higher by 10-50°C than the melting point of the medium to keep the medium liquid. This medium is fed to the head 3, while a delivery energy generator is operated according to recording signals sent from an operation circuit 5. Thus, the medium is delivered and deposited on receiving paper 7.