Examples of the compound having one oxetane ring used as component(A) are the compounds represented by the above formula (2), wherein Z represents an oxygen atom or a sulfur atom, R1 represents a hydrogen atom; fluorine atom; alkyl group having from 1 to 6 carbon atoms such as a methyl group, ethyl group, propyl group, butyl group, or the like; fluoroalkyl group having from 1 to 6 carbon atoms suc