A seating detector comprises a plurality of cells provided at a seating surface to be defined by rows and columns for detecting partial loads, an unevenness calculating means for calculating the number of cells when a partial pressure detected at the each cell is larger than a partial pressure detected at one abutting cell positioned next to the cell at one side thereof and a partial pressure detected at the other abutting cell positioned next to the cell at the other side thereof, or when a partial pressure detected at the each cell is smaller than a partial pressure detected at one abutting cell positioned next to the cell at one side thereof and a partial pressure detected at the other abutting cell positioned next to the cell at the other side thereof, and a determining means for determining that the seat is occupied by a child restraint system based on a comparison between the number of the cells and a threshold.