Provided herein are methods, systems, and apparatuses for measuring a bio-signal of a user. In one embodiment, a bio-signal measuring apparatus is provided that can operate by being combined with a plurality of target devices. For example, the bio-signal measuring apparatus can include an electrocardiogram (ECG) sensor. One or more PPG sensors can be included with a light emitting portion for generating light and a light receiving portion for receiving the light which is irradiated. The bio-signal measuring apparatus can be configured to measure one or more bio-signals using one or more of an ECG sensor and a PPG sensor, and the biological signal measuring apparatus can be configured to recognize the type of target device with which it is combined, activate a bio-signal measuring function, and correct bio-signal values.
