It is intended to provide an air-fuel ratio control device for a carburetor, which is capable of variably inject fuel by opening and closing a choke valve in accordance with an opening degree of a throttle valve and the load and which is capable of achieving low cost, clean emission and fuel saving by attaining a desired air-fuel ratio in an entire operational range (rotation speed, load) of the internal combustion engine. The air-fuel ratio control device is provided with, but not limited to, a choke valve 6 arranged in an intake path of an internal combustion engine 1, a throttle valve 7 arranged in the intake path on a downstream side of the choke valve, a first stepper motor 8 driving the choke valve 6 to adjust an opening degree of the choke valve 6, a second stepper motor 9 driving the throttle valve 7 to adjust an opening degree of the throttle valve 7, and a controller 12 controlling the opening degree of the choke valve 6 in accordance with a change of a rotation speed of the internal combustion engine 1 based on the opening degree of the throttle valve 7, and, when the rotation speed of the internal combustion engine 1 is constant, controls the opening degree of the choke valve 6 based on a map which determines the opening degree of the choke valve 6 from load of the internal combustion engine 1, so as to achieve a desired air-fuel ratio.