A headlight optical axis adjustment device for adjusting an optical axis of a headlight (30R, 30L) based on a pitch angle (θ) of a vehicle; the headlight optical axis adjustment device comprising: an opened/closed state detection section for detecting an opened/closed state of an open/close unit where the opened state is when a passenger gets in/out or when a baggage is being loaded/unloaded to and from the vehicle; a behavior detection section (20,21) for detecting a behavior change of the vehicle necessary for calculating the pitch angle (θ); an optical axis adjustment execution section (24, 25, 26, 27) for executing an adjustment of the optical axis based on the pitch angle (θ) both when the opened state of the open/close unit is detected by the opened/closed state detection section and when the closed state of the open/close unit is detected by the opened/closed state detection section; characterized in that the optical axis adjustment execution section (24, 25, 26, 27) executes the adjustment of the optical axis based on the pitch angle (θ) when judging whether or not the detection value of the behavior detection section (20, 21) is greater than a first predetermined value (Hopen) for the opened state and judged as being greater and if the opened state of the open/close unit is detected by the opened/closed state detection section, and executes the adjustment of the optical axis based on the pitch angle (θ) when judging whether or not the detection value of the behavior detection section (20, 21) is greater than a second predetermined value (Hclose) for the closed state and judged as being greater and if the closed state of the open/close unit is detected by the opened/closed state detection section. an opened/closed state detection section for detecting an opened/closed state of an open/close unit where the opened state is when a passenger gets in/out or when a baggage is being loaded/unloaded to and from the vehicle; a behavior detection section (20,21) for detecting a behavior change of the vehicle necessary for calculating the pitch angle (θ); an optical axis adjustment execution section (24, 25, 26, 27) for executing an adjustment of the optical axis based on the pitch angle (θ) both when the opened state of the open/close unit is detected by the opened/closed state detection section and when the closed state of the open/close unit is detected by the opened/closed state detection section; characterized in that the optical axis adjustment execution section (24, 25, 26, 27) executes the adjustment of the optical axis based on the pitch angle (θ) when judging whether or not the detection value of the behavior detection section (20, 21) is greater than a first predetermined value (Hopen) for the opened state and judged as being greater and if the opened state of the open/close unit is detected by the opened/closed state detection section, and executes the adjustment of the optical axis based on the pitch angle (θ) when judging whether or not the detection value of the behavior detection section (20, 21) is greater than a second predetermined value (Hclose) for the closed state and judged as being greater and if the closed state of the open/close unit is detected by the opened/closed state detection section.