An electronic device , comprising: a housing including a first surface facing in a first direction and a second surface facing in a second direction opposite the first direction, the housing including a transparent cover that comprises at least part of the first surface; a display disposed between the first surface of the housing and the second surface of the housing and configured to display information through the transparent cover to an outside; an illumination part comprising an IR LED disposed at an inner side of an end of the first surface of the housing and configured to emit IR light to the transparent cover; an optical coupler disposed between the illumination part and the transparent cover configured to reflect light emitted from the illumination part to the transparent cover; and an IR sensitive fingerprint sensor disposed under the transparent cover and the display; wherein the optical coupler is disposed under a first area of the transparent cover not overlapped by said display when viewed from above the transparent cover , and the fingerprint sensor is disposed under a second area of the transparent cover different from the first area. wherein the fingerprint sensor substantially overlaps the display when viewed from above the transparent cover , wherein the optical coupler is configured to form a first path for guiding light emitted from the illumination part to be totally reflected inside the coupler to the transparent cover , and the transparent cover is configured to form a second path for guiding the light received from the optical coupler to be reflected multiple times inside the transparent cover and configured such that when a user's fingerprint makes contact with the transparent cover in the second area, part of the light arriving by total internal reflection at this area will either be absorbed by or be scattered from the fingerprint making said contact, and part of said scattered light will be scattered in the direction of the fingerprint sensor . a housing including a first surface facing in a first direction and a second surface facing in a second direction opposite the first direction, the housing including a transparent cover that comprises at least part of the first surface; a display disposed between the first surface of the housing and the second surface of the housing and configured to display information through the transparent cover to an outside; an illumination part comprising an IR LED disposed at an inner side of an end of the first surface of the housing and configured to emit IR light to the transparent cover; an optical coupler disposed between the illumination part and the transparent cover configured to reflect light emitted from the illumination part to the transparent cover; and an IR sensitive fingerprint sensor disposed under the transparent cover and the display; wherein the optical coupler is disposed under a first area of the transparent cover not overlapped by said display when viewed from above the transparent cover , and the fingerprint sensor is disposed under a second area of the transparent cover different from the first area. wherein the fingerprint sensor substantially overlaps the display when viewed from above the transparent cover , wherein the optical coupler is configured to form a first path for guiding light emitted from the illumination part to be totally reflected inside the coupler to the transparent cover , and the transparent cover is configured to form a second path for guiding the light received from the optical coupler to be reflected multiple times inside the transparent cover and configured such that when a user's fingerprint makes contact with the transparent cover in the second area, part of the light arriving by total internal reflection at this area will either be absorbed by or be scattered from the fingerprint making said contact, and part of said scattered light will be scattered in the direction of the fingerprint sensor . <EOS>