Method for producing polyalkylene oxide

A method for producing a polyalkylene oxide, comprising

• step 1 of performing a polymerization reaction of an alkylene oxide in the presence of a chain transfer agent to obtain a high-molecular-weight polyalkylene oxide;
• and
• step 2 of irradiating the high-molecular-weight polyalkylene oxide obtained in step 1 with radiation to obtain a polyalkylene oxide;
• wherein
• the chain transfer agent is added at once in the polymerization reaction of the alkylene oxide,
• the temperature of the polymerization reaction is 35 to 50° C.,
• the amount of the chain transfer agent is 800 mass ppm or more relative to the alkylene oxide,
• the high-molecular-weight polyalkylene oxide has a viscosity in a 1 mass % aqueous solution of 6000 mPa·s or less, and
• the polyalkylene oxide obtained in step 2 has a mass average molecular weight of 100000 to 2500000, and a polydispersity of 6 or more.