[en] The author stated before that the resolution of about 20,000 is required to separate isobars which are different in atomic number Z by 1 around mass number 100, regarding the possibility to measure the mass of short-life nuclides with a high resolution mass spectrometer. In the investigation since then, however, it seems that there are many short-life nuclides in small mass number region less than 40, which are worth being measured their mass, and that the accuracy of measurement of 0.1 - 0.5 MeV is sufficient. In many cases, it is also considered that the mixing of isobars different in Z need not be feared. As a result of the above study, mass measurement seems to be significant for the time being, even if resolution is 2000 instead of 20,000. Therefore a mass spectrometer for such purposes has been designed, and it is the system with the combination of cylindrical electric field and Q-lins. Resolution of 2,000 is expected using the ion-source slit of 0.5mm in the magnetic field radius of 50cm, if a high efficiency ion source would be obtained. (Wakatsuki, Y.)