WE CLAIM:
1. A lithographic printing plate precursor comprising
an image recording layer on a hydrophilic support,
wherein the image recording layer comprises a polymerization initiator, an infrared absorbent, a polymerizable compound, and an acid color former, the infrared absorbent comprises a compound represented by the following Formula 1, and
the difference between the HOMO of the compound represented by Formula 1 and the HOMO of at least one compound of the polymerization initiator is 0.60 eV or less,
wherein Ri and R2 each independently represent a hydrogen atom or an alkyl group, Ri and R2 are optionally mutually linked to form a ring, R3 to R5 each independently represent a hydrogen atom or an alkyl group, R7 and Rg each independently represent an alkyl group or an aryl group, Yi and Y2 each independently represent an oxygen atom, a sulfur atom, -NRo-or a dialkylmethylene group, An and Ar2 each independently represent a group that forms a benzene ring or a naphthalene ring optionally having -X described below, Ai represents -NR9R10, -X1-L1, or -X described below, R9 and Rio each independently represent an alkyl group, an aryl group, an alkoxycarbonyl group, or an arylsulfonyl group, Xi represents an oxygen atom or a sulfur atom, Li represents a hydrocarbon group, a heteroaryl group, or a group where a bond with Xi is to be cleaved by heat or infrared exposure, Za represents a counter ion that neutralizes charge, and at least one of Ari or Ar2 has a group represented by the following Formula 2:
-X Formula 2
wherein X represents a halogen atom, -C(=0)-X2-Rn, -C(=0)-NRi2Ri3, -0-C(=0)-Ri4, -CN, -SO2NR15R16, or a perfluoroalkyl group, X2 represents a single bond or an oxygen atom, Rn and R14 each independently represent an alkyl group or an aryl group, and R12, R13, R15 and Ri6 each independently represent a hydrogen atom, an alkyl group, or an aryl group.
2. The lithographic printing plate precursor according to claim 1, wherein X in Formula 2 represents a fluorine atom, a chlorine atom, or -C(=0)ORi7, provided that R17 represents an

alkyl group or an aryl group.
3. The lithographic printing plate precursor according to claim 2, wherein Ai in Formula 1 represents -NRigRi9 or -S-R20, provided that Ri8 and R19 each independently represent an aryl group and R20 represents a hydrocarbon group or a heteroaryl group.
4. The lithographic printing plate precursor according to any one of claims 1 to 3, wherein the polymerization initiator is a borate compound.
5. The lithographic printing plate precursor according to claim 4, wherein the borate compound is a tetraarylborate compound or a monoalkyltriarylborate compound.
6. The lithographic printing plate precursor according to any one of claims 1 to 5, wherein the polymerization initiator comprises an electron-donating polymerization initiator and an electron-accepting polymerization initiator.
7. The lithographic printing plate precursor according to any one of claims 1 to 6, wherein the acid color former is at least one compound selected from the group consisting of a spiropyran compound, a spirooxazine compound, a spirolactone compound, and a spirolactam compound.
8. The lithographic printing plate precursor according to any one of claims 1 to 7, wherein Za represents a carbon atom-containing organic anion.
9. The lithographic printing plate precursor according to any one of claims 1 to 8, wherein Za represents a sulfonimide anion.

10. The lithographic printing plate precursor according to any one of claims 1 to 9, wherein the polymerizable compound includes a urethane-based addition-polymerizable compound.
11. The lithographic printing plate precursor according to any one of claims 1 to 10, wherein the polymerizable compound includes a compound selected from the group consisting of an ester compound of unsaturated carboxylic acid and a polyhydric alcohol compound, and an amide compound of unsaturated carboxylic acid and a polyvalent amine compound.

12. A method of preparing a lithographic printing plate, comprising
a step of imagewise exposing the lithographic printing plate precursor according to any one of claims 1 to 11 thereby forming an exposed portion and an unexposed portion, and
a step of feeding at least one of printing ink or dampening water, thereby removing the unexposed portion.