Prior to multiple reaction monitoring (MRM) measurement condition optimization, an analysis operator prepares, for each precursor ion of an objective compound, two lists on a product-ion selection condition setting screen 200, i.e. a list 203 which shows ions to be preferentially selected as product ions for which the optimization needs to be performed and a list 202 which shows ions to be excluded from the optimization. When a measurement is performed, a product-ion scan measurement for the precursor ion of the objective compound is performed and a spectrum is obtained. Among the ions extracted from this spectrum, any ion registered in the excludable-ion list 202 is excluded, while any ion registered in the preferred-ion list 203 is preferentially selected as a product ion. For each combination of the m/z values of the precursor ion and the product ions thus determined, optimum conditions of the MRM measurement are searched for.