A communication adapter (7; 54; 65) in one aspect of the present disclosure comprises a plurality of outer surfaces (7a-7f) comprising at least two outer surfaces, an interface device (22; 25), an antenna (23), and a transmission device (21). The interface device (22; 25) is provided at at least one outer surface (7b; 7f) of the at least two outer surfaces and electrically coupled to an electric working machine (2) through the at least one outer surface (7b; 7f). The antenna (23) is provided at another at least one outer surface (7a), which is different from the at least one outer surface (7b; 7f), among the plurality of outer surfaces (7a-7f), and configured to be capable of transmitting a radio wave for wireless communication with a communication device (3) other than the electric working machine (2) from the another at least one outer surface (7a).
