An apparatus for measuring a biosignal, comprising: A) a biosignal measuring sensor (110, 310, 800) comprising an optical source (120, 320, 510, 610, 810, 910) configured to emit a first light and a second light towards a target; an inserted layer (140, 340, 520, 620, 820, 920) configured to transmit the first light and to reflect the second light; and an optical detector (130, 330, 530, 630, 830, 930) 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 (140, 340, 520, 620, 820, 920); and B) a signal processor (150, 355) configured 1) to determine a) a first optical property of the first received light that varies based on a change in blood flow in the target depending on the dilatation and contraction of a blood vessel (560, 670, 860, 970) and wherein the first received light is reflected by a deep portion of the target located below a surface of the target and b) a second optical property of the second received light that varies either based on a change in surface displacement of the target depending on the dilatation and contraction of the blood vessel (560, 670, 860, 970) or based on a change in contact force of a surface of the target applied by the dilatation and contraction of the blood vessel (560, 670, 860, 970) and wherein the second received light is reflected by the inserted layer attached to a surface of the target; and characterised in that the signal processor is further configured 2) to extract biosignal information based on the first or second optical property depending on which of the first and second optical properties is determined with a higher signal quality. A) a biosignal measuring sensor (110, 310, 800) comprising an optical source (120, 320, 510, 610, 810, 910) configured to emit a first light and a second light towards a target; an inserted layer (140, 340, 520, 620, 820, 920) configured to transmit the first light and to reflect the second light; and an optical detector (130, 330, 530, 630, 830, 930) 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 (140, 340, 520, 620, 820, 920); and B) a signal processor (150, 355) configured 1) to determine a) a first optical property of the first received light that varies based on a change in blood flow in the target depending on the dilatation and contraction of a blood vessel (560, 670, 860, 970) and wherein the first received light is reflected by a deep portion of the target located below a surface of the target and b) a second optical property of the second received light that varies either based on a change in surface displacement of the target depending on the dilatation and contraction of the blood vessel (560, 670, 860, 970) or based on a change in contact force of a surface of the target applied by the dilatation and contraction of the blood vessel (560, 670, 860, 970) and wherein the second received light is reflected by the inserted layer attached to a surface of the target; and characterised in that the signal processor is further configured 2) to extract biosignal information based on the first or second optical property depending on which of the first and second optical properties is determined with a higher signal quality. 1) to determine a) a first optical property of the first received light that varies based on a change in blood flow in the target depending on the dilatation and contraction of a blood vessel (560, 670, 860, 970) and wherein the first received light is reflected by a deep portion of the target located below a surface of the target and b) a second optical property of the second received light that varies either based on a change in surface displacement of the target depending on the dilatation and contraction of the blood vessel (560, 670, 860, 970) or based on a change in contact force of a surface of the target applied by the dilatation and contraction of the blood vessel (560, 670, 860, 970) and wherein the second received light is reflected by the inserted layer attached to a surface of the target; and characterised in that the signal processor is further configured 2) to extract biosignal information based on the first or second optical property depending on which of the first and second optical properties is determined with a higher signal quality.