To allow a satisfactory coffee bean grinding work without any need of timer setting by converting the amount of coffee bean to be ground to the number of revolutions of motor speed and stopping the motor at the revolution number.

Selector switches B and C are provided as a grinding amount setting means, and respectively output signal for setting, for example, 50g and 80g. Also, a selector switch A is analog type. Furthermore, when thread intervals are at such a certain value as corresponding to a certain coarse degree of coffee bean powder, a motor is rotated, and when ground coffee powder becomes 50g, the number of motor revolutions so far obtained is totalled. This total number of motor revolutions is stored in a memory part. Then, when a grinding process starts, judgement is made as to whether the selector switch B is operating. If affirmative, data regarding an established grinding amount B is read and a motor speed corresponding to the grinding amount of 50g of the switch B is taken and read out from the memory part. Then, a counter is reset to zero and the revolutions of a motor speed is set in the counter. The motor in then started, and the number of motor revolutions is counted to see whether the number reaches the preset value. If affirmative, the motor is stopped.