An internal combustion engine comprising: an intake passage having an inlet and an intake opening, and extending from the inlet to the intake opening, the inlet being configured to introduce air, the intake opening being open to a combustion chamber; a throttle valve having a rotatable valve shaft and a valve body disposed on the valve shaft, the throttle valve being disposed inside the intake passage; a partition disposed upstream of the throttle valve of the intake passage, the partition dividing at least a portion of the intake passage upstream of the throttle valve into a first passage and a second passage, the first passage and the second passage being parallel to each other; a shut-off valve disposed inside the second passage, the shut-off valve being configured to open and close the second passage, an air cleaner; an intake pipe having the inlet and connected to the air cleaner; a throttle body housing the throttle valve and connected to the intake pipe; and a cylinder head having the intake opening and an intake port located upstream of the intake opening, the throttle body being attached to the cylinder head, an injector having an injection port from which fuel is injected, wherein the intake passage includes the intake port, the throttle body, and the intake pipe, and at least a portion of the partition is disposed inside the intake pipe, characterized in that the first passage has a channel length larger than a channel length between a downstream end of the partition of the intake passage and the valve shaft of the throttle valve, and the injector being attached to the throttle body, wherein the injection port is located at an opposite side to a center line of the second passage with respect to a center line of the throttle body when seen from a downstream side of the throttle body. an intake passage having an inlet and an intake opening, and extending from the inlet to the intake opening, the inlet being configured to introduce air, the intake opening being open to a combustion chamber; a throttle valve having a rotatable valve shaft and a valve body disposed on the valve shaft, the throttle valve being disposed inside the intake passage; a partition disposed upstream of the throttle valve of the intake passage, the partition dividing at least a portion of the intake passage upstream of the throttle valve into a first passage and a second passage, the first passage and the second passage being parallel to each other; a shut-off valve disposed inside the second passage, the shut-off valve being configured to open and close the second passage, an air cleaner; an intake pipe having the inlet and connected to the air cleaner; a throttle body housing the throttle valve and connected to the intake pipe; and a cylinder head having the intake opening and an intake port located upstream of the intake opening, the throttle body being attached to the cylinder head, an injector having an injection port from which fuel is injected, wherein the intake passage includes the intake port, the throttle body, and the intake pipe, and at least a portion of the partition is disposed inside the intake pipe, characterized in that the first passage has a channel length larger than a channel length between a downstream end of the partition of the intake passage and the valve shaft of the throttle valve, and the injector being attached to the throttle body, wherein the injection port is located at an opposite side to a center line of the second passage with respect to a center line of the throttle body when seen from a downstream side of the throttle body.