Corrosion monitoring of reinforced bar is critical for evaluating the safety and durability of concrete structures. The aim of this paper is to introduce a novel electro-magnetic monitoring apparatus (EMMA) that can be used to monitor corrosion of reinforced bar in concrete. 24 Hall-effect sensors are mounted on the novel EMMA with linearly arrangement and an enlargement monitoring probe is also equipped, by which the magnetic field intensity variation of reinforced bar/concrete interface can be detected. For comparison, the traditional electro-chemical impedance spectroscopy of the reinforced bar in concrete was recorded. As the results shown, the magnetic flux changed when corrosion occurred on reinforced bar, which further induced the increase of Hall-effect voltage at cross section of reinforced concrete. With the information of changed Hall-effect voltage, damage identification and orientation in concrete can be recorded by the EMMA. This can be used to monitor and analyze the reinforced bar corrosion in concrete time-dependently.