A vehicle system for a front-wheel drive vehicle, comprising: an engine comprising a spark plug and connecting with front road wheels; a rotary electric machine connecting with road wheels (102, 103); an operating state sensor (SN1, SN10) configured to detect an operating state of the engine; a steering wheel configured to be manipulated by a driver; a steering angle sensor configured to detect a steering angle corresponding to the manipulation of the steering wheel; and a controller configured to control the engine and the rotary electric machine, wherein the engine has a combustion mode in which a part of an air-fuel mixture in a cylinder of the engine is combusted by spark ignition of the spark plug, and then the remaining air-fuel mixture in the cylinder is combusted by self-ignition, and wherein the controller is configured: to set a target additional deceleration to be added to the vehicle, based on the steering angle detected by the steering angle sensor, when a turning manipulation of the steering wheel is performed; to set an air-fuel ratio of the air-fuel mixture to either one of a first air-fuel ratio and a second air-fuel ratio which is on a lean side with respect to the first air-fuel ratio, based on the operating state of the engine detected by the operating state sensor (SN1, SN10), when the engine is controlled to perform the combustion mode, wherein the operating state of the engine includes current values of an engine load and an engine speed; to control an ignition timing of the spark plug so as to generate the target additional deceleration in the vehicle, when the first air-fuel ratio is set; and to control a regenerative electric power generation of the rotary electric machine so as to generate the target additional deceleration in the vehicle, when the second air-fuel ratio is set. an engine comprising a spark plug and connecting with front road wheels; a rotary electric machine connecting with road wheels (102, 103); an operating state sensor (SN1, SN10) configured to detect an operating state of the engine; a steering wheel configured to be manipulated by a driver; a steering angle sensor configured to detect a steering angle corresponding to the manipulation of the steering wheel; and a controller configured to control the engine and the rotary electric machine, wherein the engine has a combustion mode in which a part of an air-fuel mixture in a cylinder of the engine is combusted by spark ignition of the spark plug, and then the remaining air-fuel mixture in the cylinder is combusted by self-ignition, and wherein the controller is configured: to set a target additional deceleration to be added to the vehicle, based on the steering angle detected by the steering angle sensor, when a turning manipulation of the steering wheel is performed; to set an air-fuel ratio of the air-fuel mixture to either one of a first air-fuel ratio and a second air-fuel ratio which is on a lean side with respect to the first air-fuel ratio, based on the operating state of the engine detected by the operating state sensor (SN1, SN10), when the engine is controlled to perform the combustion mode, wherein the operating state of the engine includes current values of an engine load and an engine speed; to control an ignition timing of the spark plug so as to generate the target additional deceleration in the vehicle, when the first air-fuel ratio is set; and to control a regenerative electric power generation of the rotary electric machine so as to generate the target additional deceleration in the vehicle, when the second air-fuel ratio is set. to set a target additional deceleration to be added to the vehicle, based on the steering angle detected by the steering angle sensor, when a turning manipulation of the steering wheel is performed; to set an air-fuel ratio of the air-fuel mixture to either one of a first air-fuel ratio and a second air-fuel ratio which is on a lean side with respect to the first air-fuel ratio, based on the operating state of the engine detected by the operating state sensor (SN1, SN10), when the engine is controlled to perform the combustion mode, wherein the operating state of the engine includes current values of an engine load and an engine speed; to control an ignition timing of the spark plug so as to generate the target additional deceleration in the vehicle, when the first air-fuel ratio is set; and to control a regenerative electric power generation of the rotary electric machine so as to generate the target additional deceleration in the vehicle, when the second air-fuel ratio is set.