Abstract: A hinge unit includes a coupler plate formed with first and second coupler holes; first and second axles extending rotatably through the coupler holes in the coupler plate and formed with first and second engaging grooves corresponding to each other; a driving slide block disposed between the first and second axles, having first and second contact surfaces formed with first and second engagement ribs in engagement with the first and the second engaging grooves such that the slide block is movable along axes of the axles; and a positioning plate formed with first and second position holes permitting extension of the first and second axles, thereby restricting a movable range of the slide block between the coupler plate and the positioning plate. Movement of the slide block along the axes of the axles results in simultaneous rotation of the axles in directions opposite to each other.