A mixer is disclosed which allows more effectively mixing and easy maintenance, and can positively and effectively suite every diversified kinds of concrete. An inside mixing blade 18 comprises first and second mixing blade elements 19, 19 each provided with a supporting member 18d for supporting mixing blades 18a. The two mixing blades 18a are each formed in helical configuration and has greater width. The first and second mixing blade elements 19, 19 are inserted to a shaft body 17a as well as a spacer 17c and prevented from coming off the shaft body 17a by a end plate 17b. In inside mixing means as structured above, the inside mixing blade 18 is formed in helical shape of substantially 360° . When any one of the mixing blades 18a is damaged, only the mixing blade element 19 having the damaged mixing blade 18a should be replaced with new one so that the replacement can be simply performed and the maintenance of the mixer 1 is improved.