Abstract: Provided is a magnesium alloy having a thermal conductivity of 75 W/m·K or more and a high specific strength. One aspect of the present invention is a magnesium alloy containing a at. % of Al, b at. % of Ca, c at. % of Mn, and d at. % of D, with the remainder comprising Mg and unavoidable impurities. D has at least one of a rare-earth element (RE), Sn, Li, Zn, Ag, Be and Sc. The magnesium alloy does not contain Si and Sr. C mentioned above satisfies expression 1 below, d satisfies expression 2 below, and a and b are within a range enclosed by the solid line shown in FIG. 1. The thermal conductivity is 75 W/m·K or greater. 0?c?0.