PURPOSE: To produce the title substance by charging an aqueous solution of compound stable to water into either one space separated by a hydrophobic porous membrane, charging a compound unstable to water into the other space and reacting both compounds through the membrane.

CONSTITUTION: A compound (B) unstable to water is permeated through a hydrophobic porous membrane into aqueous solution of compound (A) stable to water and the compound A is reacted with the compound B to produce the aimed product while suppressing hydrolysis of the compound B and produc tion of by-product. A fluorinated polymer (e.g. PTFE), preferably having 0.05-0.2μm pore size is used as a raw material for the hydrophobic porous membrane. The aimed compound expressed by formula II is produced from a compound expressed by formula I (m is 0 or 1; R1 is alkyl, etc.; R2 is alkylene; n is 0-30; l is 0 or 1; M is alkali metal), and glycidol using the above-mentioned method. The aimed compound expressed by formula II is also produced by reacting a compound expressed by formula III obtained from the compound expressed by formula I and epihalohydrin with a basic aqueous solution.