The present invention provides: a production process for an alkylene oxide addition product, by which a high-molecular alkylene oxide addition product can be obtained with ordinary production facilities while the formation of by-products is suppressed; and production processes for derivatives from the alkylene oxide addition product. The present invention production process for an alkylene oxide addition product comprises the step of carrying out an addition reaction of an alkylene oxide to a hydroxyl-group-containing saturated compound in order to obtain the alkylene oxide addition product; with the production process being characterized by further comprising: the initial step of causing the alkylene oxide to add to the hydroxyl-group-containing saturated compound in an amount of not larger than 20 mols on average of the alkylene oxide per 1 mol of the hydroxyl-group-containing saturated compound to thereby obtain an alkylene oxide low-mol-addition product; and the molar-degree-of-polyaddition-adjusting step of causing the alkylene oxide to further add to the alkylene oxide low-mol-addition product as obtained in the initial step; wherein a portion of the entirety of the alkylene oxide low-mol-addition product as obtained in the initial step is used in the molar-degree-of-polyaddition-adjusting step.