A developer comprising at least one carbonate, at least one hydrogen carbonate and at least one alkali silicate, wherein the ratio of the total molar concentration "a" of the carbonate and the hydrogen carbonate to the molar concentration "b" of the SiO.sub.2 component present in the alkali silicate: "a/b" ranges from 1:0.3 to 1:2, the total molar concentration of "a" and "b": "a+b" ranges from 0.1 to 2 mole/L, and the pH value thereof ranges from 9 to 13; and an image-forming method which comprises the steps of imagewise exposing a negative-working image-forming material which comprises a substrate provided thereon with an image-recording layer comprising an infrared light absorber, a polymerization initiator, an ethylenically unsaturated bond-containing monomer and a polymer binder, and then developing the imagewise exposed image-forming material with the foregoing developer.