To provide a support device reducing a shock when stopping a second casing in a position of a laterally long state or a longitudinally long state.

In this electronic apparatus, the second casing is openable/closable to a first casing through a support means installed movably up and down to the first casing, and the second casing is installed to the support means through a cycloid mechanism in a state that cycloid operation can be performed between the laterally long state and the longitudinally long state. The cycloid mechanism is constituted of: a base member installed to one of the second casing and the support means; a pair of guide oblong holes for the cycloid operation formed in the base member; a bracket installed to the other of the second casing and the support means, having guide shafts inserted in and engaged with the pair of guide oblong holes; and a control means controlling the cycloid operation of the bracket to the base member.