The invention provides a technology for promptly determining bacterial identification or an antimicrobial susceptibility testing. In the invention, first, a state where the bacteria are divided is monitored by performing microscopic observation with respect to the shape or the number of bacteria in each of wells of a culture plate for bacterial identification culture or the antimicrobial susceptibility testing. In addition, the shape, the number or the area of the bacteria are interpreted from the image obtained by the microscopic observation whether or not the bacteria proliferate at a stage from an induction phase to a logarithmic phase, and the time-dependent changes thereof are made into a graph. From the graph, it is determined whether or not the bacteria proliferate for each measurement, the determination results are displayed on the screen, and accordingly, the result of the antimicrobial susceptibility is provided every time when the measurement is performed (FIG. 12).