The postoperative pain of lumbar fusion surgery is very severe that it is necessary to use additional analgesics as well as a patient controlled analgesia (PCA). The most common pain control method of this surgery is the intravenous (IV) PCA. but, if it is relatively insufficient amount of narcotic analgesics ,in the case of IV PCA, may be failed to reduce the pain intensity effectively. Consequently, it may result in the a lot of rescue analgesics requirement, which leads to the adverse effects in patients who are very sensitive to narcotic analgesics. In addition, the patient's satisfaction to the PCA may be low compared with that of expected. For the recently released PCA instrument 'PAINSTOP', the investigators can specify the mode setting including total volume, flow rate (basal rate) per hour, bolus dose, and lock out time (LOT). Furthermore, this device can be set to optimize basal infusion (B.I), which is a new mode, so that the administered rate and amount of drug can be increased or decreased according to the patient's use of bolus button. Therefore, this PCA device can be implemented to the conventional mode, and added the function of automatically controlling the basal rate and administered amount of drug according to the use demand of the patient. However, since there are few studies related to this new mode of PCA, more research is needed in patients with postoperative pain.

Inclusion Criteria:

1. The subjects who undergoing lumbar fusion surgery
2. ASA class Ⅰ-Ⅲ
3. Written consents obtained to participate voluntarily in this clinical trial

Exclusion Criteria:

1. Sudden change of surgical plan
2. Patients who have the hypersensitivity to the pain killers including narcotics
3. Patients who are unable to express the degree of pain