A battery pack disclosed herein is configured to be attached to a battery pack mount by moving the same downward with respect to the battery pack mount and be detached from the battery pack mount by moving the same upward with respect to the battery pack mount. The battery pack comprises a casing. The casing includes a first guide groove and a second guide groove on a side surface of the casing in a left-right direction, with the first and second guide grooves each extending upward from a lower end of the side surface. A length of the first guide groove in an up-down direction and a length of the second guide groove in the up-down direction are different.