Tracing apparatus

A tracing apparatus communicably connected to a programmable logic controller (PLC) that inputs and outputs a signal based on a sequence control program, the tracing apparatus comprising:

• a constituent element setting unit configured to set a plurality of constituent elements to be traced among the constituent elements of the sequence control program;
• a tracing data acquisition unit configured to acquire tracing data indicating a signal state of the constituent element at a specified timing, at a predetermined sampling cycle;
• a section detection unit configured to detect a sampling cycle section in which two or more of the tracing data corresponding to the constituent elements acquired by the tracing data acquisition unit simultaneously change;
• a change sequence calculation unit configured to calculate change sequence of signals of the constituent elements simultaneously changing in the sampling cycle section detected by the section detection unit;
• and
• a change sequence output unit configured to output the change sequence of the signals of the constituent elements calculated by the change sequence calculation unit.