The invention relates to measuring the concentration of a target component in an object. The invention provides a component concentration measurement method including a first step in which light is irradiated onto a measurement object held in a first magnetic field state for detecting the light from the object, a second step in which light is irradiated onto the object held in a second magnetic field state different from the first state for detecting the light from the object, and a third step in which the concentration of the target component is calculated based on the detection results in the first and the second steps. The first magnetic field state may be a magnetic-field-modulated state, while the second state may be a non-magnetic-field-modulated state.