An amplifier selection device includes: a storage means for storing a database containing information pertaining to motor models, amplifier capacities and feature amounts; a means that obtain information of motor models necessary to configure a desired system; a means that calculate a number of necessary amplifiers; a means that select spindle amplifiers; a means that create a combination of servo amplifiers for each spindle amplifier; a means that extract information pertaining to the feature amounts by referring to the database; a means that determine a combination on a basis of the information pertaining to the feature amounts; a power source capacity calculation means that calculate capacities of a main power source and a control power source by referring to the database; and a display control means that display the combination of amplifiers along with the main power source and control power source capacities.

An amplifier selection device includes: a storage means for storing a database containing information pertaining to motor models, amplifier capacities and feature amounts; a means that obtain information of motor models necessary to configure a desired system; a means that calculate a number of necessary amplifiers; a means that select spindle amplifiers; a means that create a combination of servo amplifiers for each spindle amplifier; a means that extract information pertaining to the feature amounts by referring to the database; a means that determine a combination on a basis of the information pertaining to the feature amounts; a power source capacity calculation means that calculate capacities of a main power source and a control power source by referring to the database; and a display control means that display the combination of amplifiers along with the main power source and control power source capacities.

A rotation number detector outputs a signal based on a detection signal from a sensor, the detection signal reflecting a movement of a detected portion of a detection object. The output signal from the sensor is rectified by a comparator. A cycle measurement circuit measures a cycle of a rectangular wave signal from the comparator. A variable divider variably divides the cycle in reverse proportion to the measured cycle of the cycle measurement circuit, dividing the cycle by a smaller dividing ratio when the measured cycle becomes longer and dividing the cycle by a greater dividing ratio when the measured cycle becomes shorter. A one shot circuit converts the rectangular wave signal of the variable divider to a signal having a dividing ratio discernible wave form, which represents the dividing ratio of the variable divider, and outputs such a signal.