A blood collecting apparatus includes a main flow path and a pressure generator. The pressure generator is provided in an intermediate position of the main flow path to insert a gas as separators at designated predetermined intervals, thereby to take out blood to be measured, as separated in a time series. The blood can be taken out in minute volumes by inserting the separators consisting of the gas while feeding the blood continuously into the main flow path in this way. And consumption of the blood can be held down, and the amount of collected blood can be minimized. Since the operation to insert the separators is excellent in speed, repeated collection in a short time, i.e. frequency of blood collection, can be secured.