To provide a method and device for manufacturing a magnesium alloy plate of a fine crystal grain and of a high mechanical strength.

Magnesium alloy 28a melted in a furnace 1 is made into a linear shape 28b with a diameter of 100 μ or less and dropped on a horizontal table 11 in a chamber 10 via a nozzle 8 of a furnace bottom 1'. The horizontal table 11 is moved in a forward, backward direction (Y direction) while swinging in a left, right direction (X direction) against a dropping direction (an arrow mark a) so as to form a crowded element 28c of a linear magnesium alloy in zigzags on the table 11. By repeating the above mentioned action on the table 11, a layer of crowded element 28c in zigzags is formed to be a magnesium alloy plate of a given thickness.