A β-modified phosphoric acid compound precursor that inhibits the progress of a phosphorylation reaction having a partial structure represented by where A1 represents —SR1, —S—S—R1, —SeR1, or —X, where X is a halogen selected from fluoro, chloro, bromo, and iodo; R1 represents hydrogen, an alkyl group having 1 to 20 carbon atoms, or the like; L1 represents hydrogen, an alkyl group having 1 to 20 carbon atoms, or the like; L2 represents an alkyl group having 1 to 20 carbon atoms, or the like; L1 and L2 may be linked to each other to form a 4 to 6-membered ring structure; L1 and L2 may each have a substituent; and the symbol * represents a bond to be bonded to a phosphate group by phosphorylation. Further, provided are a reaction inhibitor and a medicine, each of which includes the β-modified phosphoric acid compound precursor.