This invention provides a biological component-measuring device, enabling the operator to easily calibrate the entire device and capable of measuring biological components accurately, and a method for calibrating the device. The device measures a sample including a body fluid taken through a body fluid sampler by sending it with a pump through a sample channel to a sensor. The device further includes a calibrating liquid channel through which a calibrating liquid can be supplied to the sensor via the sample channel by a switching of a first flow path changeover valve placed in the sample channel at a location upstream of the pump and connected to the channel. The method includes introducing the calibrating liquid in the calibrating liquid channel, via other channels, into the sensor by switching the valve.