The present invention discloses an input apparatus, a control system, a handheld apparatus and a calibration method. The input apparatus includes a casing, an output section, a processing section, a judgment section, and a calibration section. The output section includes a reference potential and outputs, as a detection signal, a fluctuation of a potential with respect to the reference potential,that corresponds to a movement of the casing. The processing section executes processing for generating a control command for controlling a screen based on an output value of the output section. The judgment section judges an operational state of the input apparatus. The calibration section executes, when it is judged that the input apparatus is moving, a calibration mode as processing for correcting the reference potential by obtaining the output value over a data obtainment period that is a sampling period of the output value and calculating a correction value of the reference potential based on the obtained output value. Reference potential of the sensor can be corrected suitably by the invention.