A circuit for adjusting a frequency of an AC direct lighting apparatus is provided. The circuit may include a reference voltage generation unit configured to receive a dimming voltage having a first frequency and a first voltage range, and generate a reference voltage having a second voltage range, a sensing section determining unit configured to generate first and second section reference voltages based on the reference voltage, and determine a driving current sensing section using the first and second section reference voltages, and a driving signal generation unit configured to generate a switching device driving signal having a second frequency through the determined driving current sensing section.