Method for producing polyether polyol and method for producing rigid foam synthetic resin

A method for producing a polyether polyol, which comprises ring-opening addition of an alkylene oxide to an initiator which is a reaction product obtainable by reacting the following phenol, the following aldehyde and the following alkanolamine, wherein

• the step of ring-opening addition of an alkylene oxide to an initiator comprises a first step of ring-opening addition of at least one member selected from propylene oxide and butylene oxide to the initiator in the absence of a catalyst, and a second step of ring-opening addition of an alkylene oxide of which at least a part is ethylene oxide, to a reaction product of the first step, in the presence of a catalyst, and
• the proportion of ethylene oxide in the total amount of the alkylene oxide to be added by the ring-opening addition to the initiator, is from 5 to 95 mol %:
• Phenol:
• at least one member selected from the group consisting of phenol and phenol derivatives wherein at least one ortho position is unsubstituted,
• Aldehyde:
• at least one member selected from the group consisting of formaldehyde and acetaldehyde,
• Alkanolamine:
• at least one member selected from the group consisting of monoethanolamine, diethanolamine and 1-amino-2-propanol.