Abstract: A method for analyzing a cause of prolonging coagulation time of a blood specimen includes: adding a calcium solution to a first sample resulting from a first waiting time from mixing of a blood specimen from a subject and a measurement reagent for an activated partial thromboplastin time; obtaining a first coagulation time and/or a first parameter regarding a differential of a coagulation waveform, for the first sample; adding the calcium solution to a second sample resulting from a second waiting time, which is longer than the first waiting time, from mixing of the blood specimen from the subject and the measurement reagent; obtaining a second coagulation time and/or a second parameter regarding a differential of a coagulation waveform, for the second sample; and obtaining information regarding a cause of prolonging a coagulation time, on the basis of the first and second coagulation time and/or the first and second parameter.