An apparatus and a method of measuring a biosignal are provided. The apparatus of measuring a biosignal includes an optical source configured to emit a first light and a second light towards a target, an inserted layer configured to transmit the first light and to reflect the second light, and an optical detector configured to detect a first received light that corresponds to the first light reflected by or transmitted through the target, and to detect a second received light that corresponds to the second light reflected by the inserted layer.