The present disclosure provides a technique related to a cooler including a main channel in which an object to be cooled is attached to an upper surface thereof, and a structure which prevents air bubbles from entering the main channel. A cooler for cooling an object may include: a main channel in which coolant flows, wherein the object is attached to an upper surface of the main channel; and a sub channel bypassing the main channel, wherein a ceiling of the sub channel is higher than a ceiling of the main channel at a branch point between the main channel and the sub channel. Air bubbles trapped in the coolant flow into the sub channel having a higher ceiling height, thus they do not enter the main channel.