The utility model relates to an energy saving device for an internal-combustion engine, which comprises an internal-combustion engine connector (1). The combustion engine connector (1) is connected with a fuel supply system (2), an air filter (3) and a gas supply system (5) in sequence; the gas supply system (5) is provided with a flow valve (9) inside; one side of the flow valve (9) is connected with a pressing plate (10) extending into a flow opening (7), and the other side of the flow valve (9) is connected with a diaphragm (11); the diaphragm (11) is connected with the shell (13) of the gas supply system (5) through a spring (12); one side of the shell (13), which is located on the spring (12), is provided with a diaphragm opening (14) and an acceleration diaphragm opening (15); and the diaphragm opening (14) and the acceleration diaphragm opening (15) are respectively connected with a negative pressure hole (17) and an acceleration negative pressure hole (18) on the fuel supply system (2) through a negative pressure control pipe (16). The energy saving device has simple structure and improves the energy saving efficiency by at least 30 percent.