The invention provides novel compounds useful as intermediates for the production of polymethine compounds containing a desired counter ion with high purity and in high yields.Thus provided are polymethine ether compounds of the general formula (I) given below and a method of producing polymethine compounds which comprises bringing those compounds into contact with an acid. In the above formula, R represents an alkyl group, an alkoxyalkyl group or an aryl group which may optionally be substituted, R1 and R2 each independently represents a hydrogen atom, halogen atom, nitro group, alkyl group, alkoxyalkyl group, alkoxy group or alkoxyalkoxy group and R1 and R2 may be bound to each other to form a ring; R3 represents an alkyl group, which may optionally be substituted; L is an alkylene group required for the formation of a ring structure; and X represents a hydrogen atom, halogen atom, alkoxy group, aryloxy group, alkylthio group, arylthio group or substituted amino group.