In a step of producing a powder product of the alga belonging to the genus Dunaliella, a pH adjusting step is included in which an alga belonging to the genus Dunaliella is allowed to be in a basic state of pH 9.5 or higher. According to the method, it is possible to provide dried Dunaliella powder containing β-carotene at a high content by suppressing degradation of β-carotene as an active ingredient while decreasing each of the total pheophorbide amount and the existing pheophorbide amount to a predetermined value or less, even if the total pheophorbide amount and the existing pheophorbide amount of the cultured algae belonging to the genus Dunaliella are higher in summer.