A method of measuring blood coagulability, comprising the following steps of:preparing a reaction solution containing a plasma specimen, a blood coagulation activator, the guanidine compound represented by the following formula (1) or an acid addition salt thereof:where R1 represents a hydrogen atom, an amino group, or an alkyl group which may have a substituent andmeasuring a coagulation time of the reaction solution by detecting a turbidity change.
