An intake system that allows air to be taken into an engine in a motorcycle, comprising: an intake passage provided on a main frame of the motorcycle and arranged to guide outside air into a cylinder in the engine; a first air cleaner element provided in the intake passage; a flow rate detector provided in the intake passage and arranged to detect a flow rate of air; and a throttle valve arranged to adjust the flow rate of air taken into the cylinder through the intake passage; wherein a combustion state in the engine is adjusted based on the flow rate of air detected by the flow rate detector characterized in that the flow rate detector is provided at an upstream side of the first air cleaner element; the intake system further comprises: a continuously variable valve device configured to drive an intake valve such that a maximum displacement of the intake valve of the engine can be continuously varied in response to an engine speed of the engine and an accelerator operation by a rider; a state detector configured to detect a state of the continuously variable valve device; and a controller configured to adjust the amount of air taken into the cylinder by controlling the continuously variable valve device; wherein the controller is configured to stop adjusting the amount of air by controlling the continuously variable valve device and start adjusting the amount of air by controlling the throttle valve when the state detector detects a prescribed state of the continuously variable valve device, and is configured to control the throttle valve such that the amount of air taken into the cylinder is reduced in a prescribed ratio when the state detector detects the prescribed state. an intake passage provided on a main frame of the motorcycle and arranged to guide outside air into a cylinder in the engine; a first air cleaner element provided in the intake passage; a flow rate detector provided in the intake passage and arranged to detect a flow rate of air; and a throttle valve arranged to adjust the flow rate of air taken into the cylinder through the intake passage; wherein a combustion state in the engine is adjusted based on the flow rate of air detected by the flow rate detector characterized in that the flow rate detector is provided at an upstream side of the first air cleaner element; the intake system further comprises: a continuously variable valve device configured to drive an intake valve such that a maximum displacement of the intake valve of the engine can be continuously varied in response to an engine speed of the engine and an accelerator operation by a rider; a state detector configured to detect a state of the continuously variable valve device; and a controller configured to adjust the amount of air taken into the cylinder by controlling the continuously variable valve device; a continuously variable valve device configured to drive an intake valve such that a maximum displacement of the intake valve of the engine can be continuously varied in response to an engine speed of the engine and an accelerator operation by a rider; a state detector configured to detect a state of the continuously variable valve device; and a controller configured to adjust the amount of air taken into the cylinder by controlling the continuously variable valve device; wherein the controller is configured to stop adjusting the amount of air by controlling the continuously variable valve device and start adjusting the amount of air by controlling the throttle valve when the state detector detects a prescribed state of the continuously variable valve device, and is configured to control the throttle valve such that the amount of air taken into the cylinder is reduced in a prescribed ratio when the state detector detects the prescribed state.