The present invention provides a curable composition including: a compound
having a single partial structure containing a cyclic ether group, and at
least one linear alkyl group having 5 or more carbon atoms; and a
compound that generates acid when irradiated with radiation. The present
invention also provides an ink composition containing the curable
composition, an inkjet-recording method by using the ink composition, and
a planographic printing plate obtained by using the ink composition.