An agitator comprising: a reactor; a rotary shaft rotatably installed in the reactor; rotor blades installed at an outer circumference of the rotary shaft and rotated with the rotary shaft to agitate a material therein; and an agitating hook (20, 120) constituted by a pair of symmetrical members which are spaced apart from each other at an inner wall of the reactor and through which the rotor blades pass, wherein the rotor blade further comprises an agitating rib perpendicularly extending from an end of the rotor blade, wherein a blade passing part through which the rotor blade passes and a rib passing part through which the agitating rib passes are formed between the pair of members of the agitating hook (20, 120), and the blade passing part has a width smaller than that of the rib passing part, wherein each member of agitating hook (20, 120) comprises: a support part (22, 122) projecting from the inner wall of the reactor at a predetermined interval, a connection part (24, 124) extending from tips of the support parts (22, 122) in facing directions; and a parallel part (26, 126) parallelly extending from tips of the connection parts (24, 124), characterised by a gap between the pair of members of agitating hook (20, 120) being larger at an outlet port through which the rotor blade leaves than at an inlet port through which the rotor blade enters, and wherein inclined surfaces (28, 28', 28") are formed at facing surfaces of the parallel parts (26, 126) so that the gap is increased from the inlet port through which the rotor enters to the outlet port, and wherein between two support parts (22, 122) of a pair of members of the agitating hook (20, 120) the rib passing part is formed, and between two parallel parts (26, 126) of a pair of members of the agitating hook (20,120) the blade passing part is formed. a reactor; a rotary shaft rotatably installed in the reactor; rotor blades installed at an outer circumference of the rotary shaft and rotated with the rotary shaft to agitate a material therein; and an agitating hook (20, 120) constituted by a pair of symmetrical members which are spaced apart from each other at an inner wall of the reactor and through which the rotor blades pass, wherein the rotor blade further comprises an agitating rib perpendicularly extending from an end of the rotor blade, wherein a blade passing part through which the rotor blade passes and a rib passing part through which the agitating rib passes are formed between the pair of members of the agitating hook (20, 120), and the blade passing part has a width smaller than that of the rib passing part, wherein each member of agitating hook (20, 120) comprises: a support part (22, 122) projecting from the inner wall of the reactor at a predetermined interval, a connection part (24, 124) extending from tips of the support parts (22, 122) in facing directions; and a parallel part (26, 126) parallelly extending from tips of the connection parts (24, 124), characterised by a gap between the pair of members of agitating hook (20, 120) being larger at an outlet port through which the rotor blade leaves than at an inlet port through which the rotor blade enters, and a support part (22, 122) projecting from the inner wall of the reactor at a predetermined interval, a connection part (24, 124) extending from tips of the support parts (22, 122) in facing directions; and a parallel part (26, 126) parallelly extending from tips of the connection parts (24, 124), characterised by a gap between the pair of members of agitating hook (20, 120) being larger at an outlet port through which the rotor blade leaves than at an inlet port through which the rotor blade enters, and wherein inclined surfaces (28, 28', 28") are formed at facing surfaces of the parallel parts (26, 126) so that the gap is increased from the inlet port through which the rotor enters to the outlet port,