On-machine development type planographic printing plate precursor, method for preparing planographic printing plate, and planographic printing method

An on-machine development type planographic printing plate precursor, comprising:

• a support;
• and
• an image-recording layer on the support,
• wherein the image-recording layer contains an initiator, an infrared absorber capable of donating electrons to the initiator, and a color-developing substance precursor having a lactone, lactam, sultone, or spiropyran skeleton,
• in a case where the image-recording layer is exposed to an infrared laser with a wavelength of 830 nm at an energy density of 110 mJ/cm2, a brightness change ΔL of the image-recording layer before and after the exposure is 3.0 or more,
• a molar light absorption coefficient e of a color-developing substance generated from the color-developing substance precursor is 35,000 or more,
• a ring-opening rate of the color-developing substance precursor calculated by the following equation is 40 mol % to 99 mol %,
• ring-opening rate=molar light absorption coefficient of the color-developing substance precursor to which 1 molar equivalent of acid is added/molar light absorption coefficient ε of a color-developing substance generated from the color-developing substance precursor×100,
• a color-developing substance generated from the color-developing substance precursor has a maximum absorption wavelength of 500 nm to 650 nm in a wavelength range of 380 nm to 750 nm.