A handheld electronic device including a first body, a second body, a sliding block and a linkage mechanism is provided. The first body is stacked on the second body. The sliding block is located between the first body and the second body, and is slidably coupled to the first body. The linkage mechanism is connected between the sliding block and the second body, by which while the first body and the second body are spread in a direction, the first body and the second body are approximately coplanar. Therefore, space in the device can be used efficiently. Besides, the device can be more miniaturized and operated more conveniently.