A blood test apparatus having a simple constitution whereby stable measurement can be conducted by surely sampling the blood in an amount being small but sufficient for the test without placing too much burden on a patient. When a first skin contact sensor of this apparatus detects the skin, driving of a negative pressure unit is initiated (time point 166a). Thus, the skin rises and comes into contact with a second skin contact sensor (time point 166b). After piercing into the skin at time point 166c, the negative pressure supply is once ceased. Next, the negative pressure is applied again at time point 166d for a definite period of time. Thus, the opening in the skin is broadened, which facilitates the flow out of the blood (16).