An automatic choke system includes: a wax-type temperature sensing section; and an output section which opens a choke valve of a carburetor in response to heat receiving operation of the temperature sensing section. Temperature sensing section includes: a bottomed cylindrical housing attached to an engine with its bottom portion directed to a high-temperature portion of the engine; a bottomed movable cylinder; a stationary piston slidably supported by the movable cylinder and having one end protruding out of the movable cylinder; and a wax contained in the movable cylinder in a sealed manner, and causing the movable cylinder and the stationary piston to move relative to each other in an axial direction. The movable cylinder is slidably housed in the housing in a state in which an outer end of the stationary piston abuts against an inner surface of the bottom portion of the housing. The output section is connected to the movable cylinder. Thus, the rate of opening of the choke valve can be increased immediately after the start of engine warming-up operation, and reduced as approaching the completion of engine warming-up operation.