Proposed are a brain signal measurement system and the like, capable of carrying out in vivo placement of measurement units for measuring brain signals with a minimally invasive operation, as well as of easily adjusting the position of each measurement unit. The brain signal measurement device includes sensors to be provided in a space between a dura mater and an arachnoid mater, and a holding unit for holding the sensors. The sensors are connected by a shape-memory unit. The sensors are inserted through a hole penetrating through the scalp and so on, into a space between the dura mater and the arachnoid mater. The diameter of the hole can be equal to or smaller than 1 cm. By electrical heating, the shape-memory unit changes its shape to change positions of the sensors, and thus subdural electrodes can be placed with a minimally invasive operation.
