A mass spectrometer includes a vacuum chamber, a turbomolecular pump, and a roughing pump. The vacuum chamber is divided into a low vacuum chamber and a high vacuum chamber respectively provided with, on their wall surfaces, a first opening and a second opening. The turbomolecular pump has an operation chamber including in its inside a blade rotor and being provided with a first intake port, and an exhaust chamber communicating with the operation chamber and being provided with a second intake port and an exhaust port. The turbomolecular pump is placed so that the high vacuum chamber and the operation chamber communicate with each other through the second opening and the first intake port, and the low vacuum chamber and the exhaust chamber communicate with each other through the first opening and the second intake port. The roughing pump is connected to the exhaust port.