A motorcycle with a drive power source, a drive power source control section (22d, 220d), a front wheel and rear wheel, said motorcycle further comprises: a target slip value calculating section for calculating a target slip value (Stg) based on an accelerator operation by a driver; an actual slip value calculating section for calculating an actual slip value (Sr), based on a difference between a rotation speed (Vf) of the front wheel and a rotation speed (Vr) of the rear wheel; the drive power source control section (22d, 220d) is adapted for controlling an output torque of the drive power source, based on a difference (ΔS1) between the actual slip value (Sr) and a criterion value different from the target slip value (Stg), and wherein the criterion value is a value lower than the target slip value (Stg); the drive power source control section (22d, 220d) includes a determining section for determining whether or not the actual slip value (Sr) is higher than the target slip value (Stg); wherein if the actual slip value (Sr) reaches the criterion value, and then reaches the target slip value (Stg): the drive power source control section (22d, 220d) is adapted for reducing the output torque of the drive power source, based on the difference (ΔS1) between the actual slip value (Sr) and the criterion value such that a reduction amount for the output torque of the drive power source increases as the actual slip value (Sr) becomes higher, when the actual slip value (Sr) is lower than the target slip value (Stg), and the drive power source control section (22d, 220d) is adapted for reducing the output torque of the drive power source, based on the difference (ΔS2) between the target slip value (Stg) and the actual slip value (Sr) when the actual slip value (Sr) is higher than the target slip value (Stg). a target slip value calculating section for calculating a target slip value (Stg) based on an accelerator operation by a driver; an actual slip value calculating section for calculating an actual slip value (Sr), based on a difference between a rotation speed (Vf) of the front wheel and a rotation speed (Vr) of the rear wheel; the drive power source control section (22d, 220d) is adapted for controlling an output torque of the drive power source, based on a difference (ΔS1) between the actual slip value (Sr) and a criterion value different from the target slip value (Stg), and wherein the criterion value is a value lower than the target slip value (Stg); the drive power source control section (22d, 220d) includes a determining section for determining whether or not the actual slip value (Sr) is higher than the target slip value (Stg); wherein if the actual slip value (Sr) reaches the criterion value, and then reaches the target slip value (Stg): the drive power source control section (22d, 220d) is adapted for reducing the output torque of the drive power source, based on the difference (ΔS1) between the actual slip value (Sr) and the criterion value such that a reduction amount for the output torque of the drive power source increases as the actual slip value (Sr) becomes higher, when the actual slip value (Sr) is lower than the target slip value (Stg), and the drive power source control section (22d, 220d) is adapted for reducing the output torque of the drive power source, based on the difference (ΔS2) between the target slip value (Stg) and the actual slip value (Sr) when the actual slip value (Sr) is higher than the target slip value (Stg).