To obtain a rotary kiln for raising the temperature of a powder and grain in which the temperature raising rate is increased by increasing the thermal conductivity for a powder and grain layer.

A flow controller 5 is disposed at the powder and grain inlet end of a cylindrical rotary kiln made of a refractory material 1. A powder and grain feeder 2 comprising a screw feeder is passed movably through the central part in order to feed in a powder and grain 4. The powder and grain 4 is transferred while turning in the kiln and heated with hot air 3 to raise the temperature thereof. The flow controller 5 comprises an outer piece and an inner piece and since a hot air path formed between both pieces is inclined and enlarged toward the inside, temperature raising rate of the powder and grain 4 can be increased by decreasing the current velocity of hot air 3 at the central part of rotation and increasing the current velocity in the vicinity of wall face or on the surface of powder and grain layer thereby increasing the thermal conductivity.