When correcting an error caused by deviation of an attitude detection device with respect to a work machine including a swing body which swings, a working implement being attached to the swing body, the attitude detection device outputting an attitude of the work machine, the error is corrected by using a first position which is a position of a part of the work machine when the work machine is in a first attitude and a second position which is a position of the part when the work machine is in a second attitude.