To provide a soil improving material feeder capable of suppressing the lowering of accuracy in feeding a soil improving material when filling the soil improving material.

This soil improving material feeder 14 used for a soil improving machine for improving sediment by mixing the soil improving material includes: a storage tank 15 for storing the soil improving material; a chute 17 continuously provided to the lower part of the storage tank 15 and reduced in diameter downward; a cylindrical casing 61 in a lower part of the chute 17; a screw feeder 16 which comprises a rotating shaft 66 running through the inside of the casing 61 and a screw 62 provided on the outer peripheral part of the rotating shaft 66 and feeds the soil improving material in the storage tank 15 introduced by the chute 17 to the sediment; and partition plates 80, 81 which are installed in the chute 17 and partition the lower opening 55 for feeding the soil improving material to the screw feeder 16 in the chute 17 in the direction in which the soil improving material is transferred by the screw feeder 16.