Oxime ester compound and photopolymerization initiator containing such compound

An oxime ester compound represented below is useful as a photopolymerization initiator. A photopolymerization initiator including this as an active constituent has high sensitivity and causes no concern about coloration or contamination. (X represents a halogen atom or alkyl group. R1, R2, and R3 each independently represent R, OR, COR, SR, CONRR′, or CN, wherein R and R′ each represent an alkyl group, an aryl group, an aralkyl group, or a heterocyclic group; these groups may be substituted with (a) halogen atom(s) and/or (a) heterocyclic group(s); the alkylene moiety in the alkyl or aralkyl group may be interrupted by (an) unsaturated bond(s), (an) ether bond(s), (a) thioether bond(s), or (an) ester bond(s); and R and R′ may form a ring. Y1 represents an oxygen, sulfur, or selenium atom; A represents a heterocyclic group; m represents an integer 0-4; p represents an integer 0-5; and q represents 0 or 1.)