The system (9) has pressure sensor (11) that performs time-resolved detection of ventricular internal pressure. An evaluation device (12) has heart rate analysis module (14) that analyzes heart rate of patient. A shaft-phase extraction module (15) determines start and end time of synchronous heart rate intracranial pressure wave. A waveform analysis module (16) assigns intracranial pressure wave of specific waveform from waveform candidates. A control signal generation module (21) generates drain-control signal based on allocation result of waveform analysis module.