Treatment of tennis elbow includes relative rest, physical therapy (therapeutic exercise, massage, therapeutic ultrasound, lower power laser, etc.), analgesics, non-steroidal anti-inflammatory drugs, glyceryl trinitrate patches, injection therapy (corticosteroid, hyaluronan gel, botulinum toxin, and autologous platelet-rich plasma), shock wave therapy, and even surgery. Previous studies showed corticosteroid injection is effective in the short term, but is harmful in the long-term, and is more likely to have a recurrence. In consideration of a degenerative lesion in tennis elbow, corticosteroid injection may be not an ideal agent. Although plate-rich plasma injection showed promising results, the high cost limited its widespread clinical use. Since local lidocain injection is commonly used in the management of myofascial pain syndrome, it might be effective in the treatment of tendinopathy like tennis elbow. The purpose of this study is to compare the effect of corticosteroid injection and lidocain injection in the treatment of tennis elbow. The investigators hypothesized that lidocain injection is as effective as corticosteroid injection in management of tennis elbow, and if so, it may replace corticosteroid injection in the management of tennis elbow.