An optical concentration measuring device capable of power saving and lifespan extension of a light source is provided, including a light source emitting an amount of light corresponding to a supplied power; a light detection part receiving at least a part of the light emitted by the light source and generating a signal corresponding an amount of received light as an output signal; a smoothing filter smoothing a signal based on the output signal; a signal change amount calculation part calculating a first and a second change amounts corresponding to a change amount between at least two selected acquisition values selected from acquisition values based on the output signal at current or past time; a light source control part controlling the power supplied to the light source based on the first change amount; and a filter control part controlling characteristics of the smoothing filter based on the second change amount.