A solid phase immunoassay using an antigen or/and an antibody immobilized onto fine solid carriers dispersible in a liquid medium, comprising a chemiluminescence method used for signal detection which comprises reacting a chemiluminescent substrate having dioxetane with acid phosphatase, alkali phosphatase, glucosidase, glucuronidase or esterase as an enzyme of a labeled body in the presence of a chemiluminescence enhancer, wherein the chemiluminescence enhancer is the one which is obtained by treating a water soluble polymer represented by following general formula: wherein, each of R 5, R 6 and R 7 is a straight or branched, unsubstituted alkyl group having 1 to 20 carbon atoms; a straight or branched alkyl group having 1 to 20 carbon atoms substituted with one or more of a hydroxyl group, an alkoxy group, an aryloxy group, an amino group, a substituted amino group, an amide group or an ureide group; a fluoroalkane group; a fluoroaryl group; an unsubstituted monocycloalkyl group having 3 to 12 ring carbon atoms; a substituted monocycloalkyl group having 3 to 12 ring carbon atoms substituted with one or more of an alkyl group, an alkoxy group or a condensed benzo group; polycycloalkyl group having two or more condensed rings each having 5 to 12 carbon atoms, which is unsubstituted or substituted with one or more of an alkyl group, an alkoxy group or an aryl group; an aryl group, an alkaryl group or an aralkyl group having at least one ring and totally 6 to 20 carbon atoms, which is unsubstituted or substituted with one or more of an alkyl group, an aryl group, fluorine or a hydroxyl group, or at least two of R 5, R 6 and R 7 mean the groups capable of forming together with a quaternary atom to which they are bound a saturated or unsaturated, unsubstituted or substituted ring having 3 to 5 carbon atoms and 1 to 3 heteroatoms and containing nitrogen, phosphorus or sulfur, to which a benzene ring may be condensed, Y alone or in combination represents a counter ion selected from the group consisting of a halogen ion, sulfate ion, alkyl sulfonate ion, aryl sulfonate ion, substituted aryl sulfonate ion, diphenylantracene sulfonate ion, perchlorate ion, alkanoate ion, aryl carboxylate ion, benzene heterocyclic aryl carboxylate ion and organic dianions, n represents a number over the range of 500 to 500,000 (average molecular weight), which is measured using an intrinsic viscosity or an LALLS method, M is nitrogen or phosphorus, or the water soluble copolymer of formula: wherein Y, M', R 5 ', R 6 ' and R 7 ' are the same as defined above Y, M, R 5, R 6 and R 7, and y and z represent a molar fraction of an individual monomer which constitutes the copolymer with an oxidizing agent or a reducing agent, thereby inhibiting the aggregation of the fine solid carriers, wherein the oxidizing agent or the reducing agent is selected from the group consisting of ammonium persulfate, sodium sulfite, sodium hypochlorite, hydrogen peroxide, sodium metaperiodate, potassium permanganate and potassium dichromate. each of R 5, R 6 and R 7 is a straight or branched, unsubstituted alkyl group having 1 to 20 carbon atoms; a straight or branched alkyl group having 1 to 20 carbon atoms substituted with one or more of a hydroxyl group, an alkoxy group, an aryloxy group, an amino group, a substituted amino group, an amide group or an ureide group; a fluoroalkane group; a fluoroaryl group; an unsubstituted monocycloalkyl group having 3 to 12 ring carbon atoms; a substituted monocycloalkyl group having 3 to 12 ring carbon atoms substituted with one or more of an alkyl group, an alkoxy group or a condensed benzo group; polycycloalkyl group having two or more condensed rings each having 5 to 12 carbon atoms, which is unsubstituted or substituted with one or more of an alkyl group, an alkoxy group or an aryl group; an aryl group, an alkaryl group or an aralkyl group having at least one ring and totally 6 to 20 carbon atoms, which is unsubstituted or substituted with one or more of an alkyl group, an aryl group, fluorine or a hydroxyl group, or at least two of R 5, R 6 and R 7 mean the groups capable of forming together with a quaternary atom to which they are bound a saturated or unsaturated, unsubstituted or substituted ring having 3 to 5 carbon atoms and 1 to 3 heteroatoms and containing nitrogen, phosphorus or sulfur, to which a benzene ring may be condensed, Y alone or in combination represents a counter ion selected from the group consisting of a halogen ion, sulfate ion, alkyl sulfonate ion, aryl sulfonate ion, substituted aryl sulfonate ion, diphenylantracene sulfonate ion, perchlorate ion, alkanoate ion, aryl carboxylate ion, benzene heterocyclic aryl carboxylate ion and organic dianions, n represents a number over the range of 500 to 500,000 (average molecular weight), which is measured using an intrinsic viscosity or an LALLS method, M is nitrogen or phosphorus,