A portable electronic device adapted to be detachably connected to a cradle having a containing cavity is provided, wherein an inner wall of the containing cavity has a recess. The portable electronic device includes a body and a locking-and-releasing mechanism disposed in the body and including a driving unit and a latch. The driving unit is disposed in the body. The latch is connected to the driving unit and suitable for being driven by the driving unit to protrude out of the body or hide in the body. When the portable electronic device is disposed in the containing cavity, the driving unit drives the latch to protrude out of the body and be engaged with the recess. When the portable electronic device is going to be detached from the containing cavity, the driving unit drives the latch to be disengaged from the recess and move back in the body.