Inclusion Criteria:  Diagnosed with idiopathic Parkinson's disease with freezing of gait according to the United Kingdom (UK) Brain Bank. Scored more than 15 points of Korean version of mini-mental status exam (K-MMSE). Independent gait for at least a minute without walking assistance device.  Exclusion Criteria:  History of concomitant brain disease other than idiopathic Parkinson's disease. Other neurologically deteriorated states, such as neuromuscular disease, which can cause gait disturbance. Other psychiatric disorders.