A positional information determining apparatus capable of reducing power consumption markedly in simple structure in radio transmission of positioning results to a navigation device. The user thereby selects a first image data element of a first facial section of a human face and a first image data element of a second facial section of a human face. 05 \u03bcm to about 2 \u03bcm, and the grain size of the piezoelectric layer is preferably configured to be in the range from about 1 nm to about 50 nm. The optical substrate is substantially transparent to light within the operative wavelength range. When the received radio communication data is addressed to the local device, a communicationresponse information generation unit correlates the identifier to the reservation time slot, records them in a communication reservation table, and generates communication time reservation response information including information of the reservation time slot. In another embodiment, the bottom support pad comprises an inclined surface.