A case making machine is provided with an apparatus for folding rear portion of a feeding case blank and the apparatus comprises a claw mechanism for folding the rear portion of the case blank along the folding line. The claw mechanism is rotated at an angular speed which is changed by a cam mechanism operated by a driving source through a drive shaft and a link mechanism. An electromagnetic valve is further provided for controlling the operation of the claw mechanism. The valve is actuated by an electric circuit such that the electromagnetic valve can be operated in synchrony with the advancing speed of the blank. This result is achieved by increasing pulse numbers inputted into the circuit to account for the rise time interval of the electromagnetic valve.