is fitted in the axial bore 51 of the rotation member 5 after fitted with the torsion spring 52 over the outside the other end of the rotation member 5 is pivotally fitted in the pivot hole 12 of the base 1 so that a connecting strap 432 for connecting each slat of the window blind is fixed in the locating recess 43 by the direct fastening of two screw elements 441 through the lid 44 referring to fig5 when a connecting string 433 is used to connect each slat of the window blind the connecting string 433 can be placed in the clipping grooves 431 provided at both sides of the locating recess 43 and then the connecting string 433 is similarly fixed in the locating recess 43 by the direct fastening of two screw elements 441 through the lid 44 referring to fig6 when the axle rod 421 penetrating through the shaft portion 42 of the housing member 4 and fitted in the axle portions 33 of the cord spool 3 is rotated the rotation member 5 can be rotated and the leg of the torsion spring 52 moves the protruding portion 45 of the housing member 4 to turn an angle so that the connecting strap 432 fixed in the locating recess 43 rotates the slats 434 in unison the same angle then the housing member 4 is limited by the torsion spring.