MANUFACTURING METHOD FOR PROPYLENE POLYMER

An object is to develop a method for stably producing a propylene-based polymer together with inhibiting generation of an aggregated polymer, reducing a generation amount of fine powder, and thereby enhancing production efficiency. The present invention relates to a method for producing a propylene-based polymer, comprising polymerizing propylene or propylene and an ±-olefin except propylene in the presence of a catalyst using a horizontal polymerization reactor equipped with a stirrer rotating around a horizontal axis in the inside of the reactor by a continuous vapor-phase polymerization method in which heat of reaction is removed by heat of vaporization of liquefied propylene, wherein the reactor can set a plurality of area sections different in temperature in a horizontal axis direction in the inside of the reactor and at least one of the following requirements (A) and (B) is satisfied: requirement (A): temperature difference ”T1 (°C) (= TÉ - T±) between temperature (T±) of an area section including an upstream end of the reactor and temperature (TÉ) of an area section including a downstream end thereof is 0.1 to 20°C; requirement (B): temperature difference ”T2 (°C) (= Tx - Tz) between temperature (Tx) of an area section including a catalyst feed part and dew point (Tz) of mix gas in the reactor is 0 to 5°C.