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 (A1) larger than a channel length (B) 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 (C2) of the second passage with respect to a center line (C4) 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 (A1) larger than a channel length (B) 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 (C2) of the second passage with respect to a center line (C4) of the throttle body when seen from a downstream side of the throttle body . <EOS>