A position detecting device in which a count value is incremented or decremented on the basis of a pulse output from an encoder every predetermined shift amount of a control target to thereby detect a current value representing a current position of the control target as the count value, is characterized by comprising: initialization signal output means for outputting an initialization signal representing an initialization position at plural positions of a movable range of the control target when the movable range of the control target is restricted, or at plural positions of an operating range of integer times of a period when the movable range of the control target is not restricted and the same state is repeated at the period concerned; current value storing means for storing, in association with identification information for identifying each initialization signal, the current value of the control target at each position where the initialization signal is output by each initialization signal output means; and count value setting means for moving the control target to a position where some initialization signal is output from the initialization signal output means at the initialization time of the count value, and achieving the current value corresponding to identification information for identifying the initialization signal from the current value storage means, and setting the current value thus achieved as the count value.