To efficiently perform the testing of an input or output stream.

Storage means 11 stores state transition information 11a indicating multiple states, transition between the states to each of which a symbol as a transition condition is corresponding to and an acceptance state among the multiple states. Extraction means 12 extracts the symbol included in at least one of a return value and an argument, when each of multiple times of calls of a function is performed. When the symbol is extracted at the extraction means 12, detection means 13 updates a current state according to the transition indicated by the state transition information 11a, based on the current state among the multiple states and the extracted symbol, and outputs information of the detection result of a symbol string according to whether or not the current state after an update is the acceptance state.