A wearable device includes a case, a bio-processor embedded in the case, and a plurality of electrodes connected to the bio-processor. The bio-processor is configured to selectively and respectively operate the electrodes as sensing electrodes and sourcing electrodes in response to a selection signal. The selected one/ones of the electrodes operated as sensing electrodes which pick up a biological signal from (e.g. biological activity or a biological condition of) the wearer. The selected one/ones of the electrodes operated as sourcing electrodes supply current to the wearer regulated to cause the desired biological signal to be picked up by the sensing electrode(s).