To provide a thin portable electronic apparatus in which a substrate can be prevented from being bent largely due to a user's key operation.

In this portable electronic device, a battery holder 15 is formed as a recess on the backside of a body cabinet 1, and a battery pack is housed in the battery holder 15. The battery holder 15 is constituted by a bottom wall 40 stuck on the surface of the battery pack, four side walls 41, 42, 43 and 44 for surrounding the four sides of the battery pack. The two side walls 41, 42 each cross two regions where two domes 71a, 71e formed on both ends of a dome sheet 7 disposed on the front surface of a substrate 6 are projected to the operating direction of a key operating force into the inside of the cabinet 1.