An apparatus configured to detect a light signal, the apparatus comprising: a light source configured to radiate light toward an object; a light receiver configured to receive an ambient light and a transmitted light corresponding to the light radiated toward the object from the light source; at least one processor configured to control the light source to be turned off such that a first output signal is generated by the light receiver and control the light source to be turned on such that a second output signal is generated by the light receiver; and an operator configured to generate a transmitted light signal from which noise is removed by differentially operating the second output signal from the first output signal , characterised in that the operator is further configured to: reduce a ramp signal (V RAMP ) when the first output signal is received; perform a first counting from a time when the ramp signal (V RAMP ) is reduced to a time when a magnitude of the ramp signal (V RAMP ) is less than or equal to a magnitude of the first output signal ; reduce the ramp signal (V RAMP ) when the second output signal is received; and perform a second counting from the time when the ramp signal (V RAMP ) is reduced to a time when the magnitude of the ramp signal (V RAMP ) is less than or equal to a magnitude of the second output signal , wherein the second counting starts from a stored result of the first counting, wherein the first counting and the second counting are in different directions. a light source configured to radiate light toward an object; a light receiver configured to receive an ambient light and a transmitted light corresponding to the light radiated toward the object from the light source; at least one processor configured to control the light source to be turned off such that a first output signal is generated by the light receiver and control the light source to be turned on such that a second output signal is generated by the light receiver; and an operator configured to generate a transmitted light signal from which noise is removed by differentially operating the second output signal from the first output signal , characterised in that the operator is further configured to: reduce a ramp signal (V RAMP ) when the first output signal is received; perform a first counting from a time when the ramp signal (V RAMP ) is reduced to a time when a magnitude of the ramp signal (V RAMP ) is less than or equal to a magnitude of the first output signal ; reduce the ramp signal (V RAMP ) when the second output signal is received; and perform a second counting from the time when the ramp signal (V RAMP ) is reduced to a time when the magnitude of the ramp signal (V RAMP ) is less than or equal to a magnitude of the second output signal , wherein the second counting starts from a stored result of the first counting, wherein the first counting and the second counting are in different directions. reduce a ramp signal (V RAMP ) when the first output signal is received; perform a first counting from a time when the ramp signal (V RAMP ) is reduced to a time when a magnitude of the ramp signal (V RAMP ) is less than or equal to a magnitude of the first output signal ; reduce the ramp signal (V RAMP ) when the second output signal is received; and perform a second counting from the time when the ramp signal (V RAMP ) is reduced to a time when the magnitude of the ramp signal (V RAMP ) is less than or equal to a magnitude of the second output signal , wherein the second counting starts from a stored result of the first counting, wherein the first counting and the second counting are in different directions. <EOS>