A light distribution-controlling device of a vehicle headlight, comprising: a headlight lamp body (2L, 2R) that switches light distribution to any one of a low beam state and a high beam state; a passing switch having a momentary mechanism to self-return to a neutral position when a driver terminates a passing operation and removes the driver's hand from the passing switch, a light distribution operation switch that includes the passing switch, and switches light distribution of the headlight lamp body by the driver's operation; a front detection unit that detects an object in front of an own vehicle; a manual mode control unit that controls the light distribution of the headlight lamp body based on a signal output from the light distribution operation switch; an auto mode control unit that controls the light distribution of the headlight lamp body based on a signal output from the front detection unit; an auto mode changeover switch that switches control of the light distribution of the headlight lamp body to control by the auto mode control unit by the driver's operation; a passing continuation-determining unit that determines whether a continuation time (Tp) of an ON operation of the passing switch is more than or equal to a threshold continuation time (Tpa); and an auto mode-returning unit that returns the control of the light distribution to the control by the auto mode control unit when the continuation time (Tp) is determined to be more than or equal to the threshold continuation time (Tpa) by the passing continuation-determining unit after the control of the light distribution by the auto mode control unit is switched to control of the light distribution by the manual mode control unit by an operation on the light distribution operation switch in a case in which the auto mode changeover switch is in an ON state. a headlight lamp body (2L, 2R) that switches light distribution to any one of a low beam state and a high beam state; a passing switch having a momentary mechanism to self-return to a neutral position when a driver terminates a passing operation and removes the driver's hand from the passing switch, a light distribution operation switch that includes the passing switch, and switches light distribution of the headlight lamp body by the driver's operation; a front detection unit that detects an object in front of an own vehicle; a manual mode control unit that controls the light distribution of the headlight lamp body based on a signal output from the light distribution operation switch; an auto mode control unit that controls the light distribution of the headlight lamp body based on a signal output from the front detection unit; an auto mode changeover switch that switches control of the light distribution of the headlight lamp body to control by the auto mode control unit by the driver's operation; a passing continuation-determining unit that determines whether a continuation time (Tp) of an ON operation of the passing switch is more than or equal to a threshold continuation time (Tpa); and an auto mode-returning unit that returns the control of the light distribution to the control by the auto mode control unit when the continuation time (Tp) is determined to be more than or equal to the threshold continuation time (Tpa) by the passing continuation-determining unit after the control of the light distribution by the auto mode control unit is switched to control of the light distribution by the manual mode control unit by an operation on the light distribution operation switch in a case in which the auto mode changeover switch is in an ON state.