A body fluid constituents measurement device, which performs measurement under a setting where light intensity of the light-emitting element is suitably stabilized, is provided. The present invention is a body fluid constituents measurement device which comprises: a light-emitting element that emits light onto a test paper onto which body fluid is spotted, a light receiving element which receives reflected light of the light emitted by said light-emitting element, a temperature measurement unit which measures the ambient temperature in the vicinity of said light-emitting element, a determination unit which determines conditions of light emission based on said temperature measured at said temperature measurement unit in order to stabilize light intensity of said light-emitting element, and a driving control unit which controls driving of said light-emitting element based on the conditions of light emission; and is characterized in that it starts measurement of body fluid constituents after the light intensity of light emitted by said light-emitting element has been stabilized.