The invention provides an automatic levelling control technology which can obtain the tilt angle of a vehicle from a tilt detection device more accurately and adjust the optical axis position of a vehicle lamp. An illumination control section (228) is provided with a reception section (228L1, 228R1), a control section (228L2, 228R2) and a transmission section (228L3, 228R3). The reception section (228L1, 228R1) receives a tilt angle of a vehicle (300) relative to a horizontal plane from an accelerated speed sensor (316). The control section (228L2, 228R2) corrects the tilt angle obtained from the accelerated speed sensor (316) based on correction information obtained from a pre-recorded first reference tilt angle of the vehicle (300) in a first state and a pre-recorded second reference tilt angle of the vehicle (300) in a second state different from the first state only in a pitch angle, and also determines the optical axis position of the vehicle lamp. The transmission section (228L3, 228R3) transmits the determined optical axis position to an optical axis adjustment section (236).