An engine system, comprising: a cylinder block and a cylinder head configured to form a cylinder; a piston reciprocatably accommodated in the cylinder; a main combustion chamber defined by the cylinder block, the cylinder head, and the piston; a subchamber that is separated from the main combustion chamber by a partition, and configured to communicate with the main combustion chamber through a communicating hole formed in the partition; an injector configured to inject fuel into the main combustion chamber; a main spark plug configured to ignite a mixture gas inside the main combustion chamber; a subspark plug configured to ignite the mixture gas inside the subchamber; and a control device that is electrically connected to, and configured to output an electric signal for control to, the injector, the main spark plug, and the subspark plug, wherein when an engine is operated in a specific range where an engine speed is below a given reference engine speed and an engine load is above a given reference load, the control device is configured to: control the injector so that a fuel injection timing that is an injection timing of fuel by the injector is included in compression stroke, and cause the main spark plug and the subspark plug to perform ignitions after the fuel injection timing; when two conditions in the specific range where the engine loads are the same and the engine speeds are different include a first-speed condition where the engine speed is lower and a second-speed condition where the engine speed is higher, control the injector so that the fuel injection timing under the first-speed condition becomes later than the fuel injection timing under the second-speed condition; and control the main spark plug and the subspark plug so that a subignition timing (ts) that is an ignition timing of the subspark plug becomes a timing on the retarding side of a main ignition timing (tm) that is an ignition timing of the main spark plug, and an ignition phase difference (dt) that is a retard amount of the subignition timing (ts) with respect to the main ignition timing (tm) becomes larger under the first-speed condition than under the second-speed condition. a cylinder block and a cylinder head configured to form a cylinder; a piston reciprocatably accommodated in the cylinder; a main combustion chamber defined by the cylinder block, the cylinder head, and the piston; a subchamber that is separated from the main combustion chamber by a partition, and configured to communicate with the main combustion chamber through a communicating hole formed in the partition; an injector configured to inject fuel into the main combustion chamber; a main spark plug configured to ignite a mixture gas inside the main combustion chamber; a subspark plug configured to ignite the mixture gas inside the subchamber; and a control device that is electrically connected to, and configured to output an electric signal for control to, the injector, the main spark plug, and the subspark plug, wherein when an engine is operated in a specific range where an engine speed is below a given reference engine speed and an engine load is above a given reference load, the control device is configured to: control the injector so that a fuel injection timing that is an injection timing of fuel by the injector is included in compression stroke, and cause the main spark plug and the subspark plug to perform ignitions after the fuel injection timing; when two conditions in the specific range where the engine loads are the same and the engine speeds are different include a first-speed condition where the engine speed is lower and a second-speed condition where the engine speed is higher, control the injector so that the fuel injection timing under the first-speed condition becomes later than the fuel injection timing under the second-speed condition; and control the main spark plug and the subspark plug so that a subignition timing (ts) that is an ignition timing of the subspark plug becomes a timing on the retarding side of a main ignition timing (tm) that is an ignition timing of the main spark plug, and an ignition phase difference (dt) that is a retard amount of the subignition timing (ts) with respect to the main ignition timing (tm) becomes larger under the first-speed condition than under the second-speed condition. control the injector so that a fuel injection timing that is an injection timing of fuel by the injector is included in compression stroke, and cause the main spark plug and the subspark plug to perform ignitions after the fuel injection timing; when two conditions in the specific range where the engine loads are the same and the engine speeds are different include a first-speed condition where the engine speed is lower and a second-speed condition where the engine speed is higher, control the injector so that the fuel injection timing under the first-speed condition becomes later than the fuel injection timing under the second-speed condition; and control the main spark plug and the subspark plug so that a subignition timing (ts) that is an ignition timing of the subspark plug becomes a timing on the retarding side of a main ignition timing (tm) that is an ignition timing of the main spark plug, and an ignition phase difference (dt) that is a retard amount of the subignition timing (ts) with respect to the main ignition timing (tm) becomes larger under the first-speed condition than under the second-speed condition.