PROBLEM TO BE SOLVED: To provide a bioelectrode adapter that enables a bioelectric signal acquisition device to automatically set an operation mode corresponding to a bioelectrode, and a bioelectric signal acquisition device using the same.SOLUTION: There is provided a bioelectrode adapter for connecting a bioelectrode for acquiring a predetermined bioelectric signal to a bioelectric signal acquisition device such as an electro-cardiograph. The bioelectrode adapter is configured so as to provide identification information on the bioelectrode adapter to the bioelectric signal acquisition device by a voltage of a specific pin of a connector connected to the bioelectric signal acquisition device, for example.