Magnesium alloy sheets have low formability at room temperature due to their hexagonal closed-packed microstructures. In order to increase the formability of magnesium alloy sheets (AZ31) and fabricate a complex geometry, an incremental forming process with external heat sources such as the near-infrared heater and heated tools can be employed. Cylindrical cup shapes and Pyramidal cup shapes with various angles were fabricated to find out the formability limits. The maximum formable angle of the cylindrical cup shape increased from 20 degrees at the room temperature to 72 degrees by employing the incremental forming process using two external heat sources. It means that the temperature of AZ31 was increased to a proper forming temperature very efficiently.