The object of the invention is to provide a mini-electronic device and an opening/closing device thereof. When a first housing and a second housing are turned to an opening state through a sliding means, and the second housing is upturned relative to the first housing, lead wires can be covered and hidden and are invisible from the rear of the mini-electronic device. The opening/closing device of the mini-electronic device comprises the sliding means, a connection means and a friction means. The sliding means is configured to move the first housing and a second housing along horizontal direction, and the second housing can either cover or reveal the upper surface of the first housing. The connection means is configured in such a manner that the second housing can continue to slide and to be upturned relative to the first housing and cover the gaps between the rear part of the first housing and the rear part of the second housing, after revealing of the upper surface of the first housing is completed. The friction means is arranged between the sliding means and the connection means and is active during upturning the second housing.