Calibration system, work machine, and calibration method

A calibration system comprising:

• a first position detecting unit which is provided in a work machine including a working implement so as to detect a position of an object;
• and
• a processing unit which obtains and outputs (i) a conversion information item used to convert the position detected by the first position detecting unit from a coordinate system of the first position detecting unit into a coordinate system different from the coordinate system of the first position detecting unit or (ii) a conversion information item used to convert the position detected by a second position detecting unit, which is different from the first position detecting unit, from a coordinate system of the second position detecting unit into a coordinate system different from the coordinate system of the second position detecting unit, by using a first position information item as an information item for a predetermined position of the work machine detected by the first position detecting unit and a second position information item as an information item for the predetermined position detected by the second position detecting unit in a same posture of the work machine when the first position detecting unit detects the predetermined position.