7  5,925,690  8  The amount of the phosphoric acid group-containing  monomer  (A)  used in the present invention is 0.5 to 50% by  weight, preferably 5 to 50% by weight, more preferably 7 to  40% by weight, based on the total of all the constituent  components.  If the amount of the monomer is too small,  adhesive strength to both enamel and dentin, particularly  adhesive strength to enamel, will deteriorate, whereas if the  amount is too large, adhesive strength to both enamel and  dentin, particularly adhesive strength to dentin, will dete› riorate.  A  mixture of a plurality of the above phosphoric acid  group-containing monomers can be used as required.  Among the above phosphoric acid group-contammg  monomers, preferred are phosphoric acid group-containing  monomers represented by the general formulas (2) and (3),  particularly phosphoric acid group-containing monomers  represented by the general formula (3) in which one of the  esters is an aromatic ester, from a view point of adhesive  strength to a tooth.  Illustrative examples of the pyrophosphoric acid deriva› tive in which two of the compounds represented by the  general formulas (1), (2) and (3) are condensed in the form  of  -P-0-P- through an oxygen atom are as follows.  11  [  CH2=C-C02-CH2CH2-0-P-OH  I  R2  0  I  I  CH2=C-C02-CH2CH2-o- 11$^{-oH }$ 0  11  [  CH2=c-cor+CH2+,;;o-,-OH  R2  0  I  I  CH2=C-C02-+CH2,;;-0-P-OH  II  0  11  [  - CH2=C-C02-+CH2,;;-0-,-o--O  R2  0  I  I  CH2=C-C02-+CH2-¾-o- 11$^{-oH }$ 0  11  [  - CHr-C-C02-CH2CHrO-,-O-O-OCH3  1 2  1  - CHr-C-C02-CH2CHro-ri-o-O-ocH3  0  In the general formula (3), R$_{5 }$ is selected from the group  consisting of hydrogen atom, an alkyl group having 1 to 5  carbon atoms and an alkoxyl group having 1 to 5 carbon  atoms, with examples thereof including methyl, ethyl,  propyl, isopropyl, butyl, pentyl, methoxy, ethoxy, propoxy  and the like.  Preferred examples of the phosphoric acid group› containing monomer represented by the general formula (3)  are as follows.  1 1  IT  - CH 2 =c-cor+CH2+ioo- 1 -o--Q  OH 