To access a measurement space located at the center of the magnet, an access port is provided in the direction of the magnet's axis, a clearance is provided in the coil winding portion, and another access port passes through the clearance so that a sample can be positioned perpendicularly to the coil axis. According to this configuration, an access port passing through the coil winding portion can be smaller than the access port passing through the coil axis, a sample is inserted from the access port, and a probe is inserted from the access port passing through the magnet axis, and thus the clearance can be minimized.