To provide a capacitance detecting type sleep sensor capable of precisely detecting the motion of a person in sleep.

A support plate 145 is joined to the lower face of a lower face portion 141c of an outside electrode sheet 141 so that, even if the load of a sleeper is applied to the lower face portion 141c, the load is received by the support plate to prevent the deformation of the lower face portion 141c. That is to say, even if this capacitance detecting type sleep sensor 14 is installed on bedding, the support plate 145 receives the load from the sleeper (the bedding is prevented from absorbing the load from the sleeper) so that the upper face portion 141a of the outside electrode sheet 141 deforms by the loading from the sleeper. The capacitance between the electrode sheet is therefore appropriately changed according to the loading from the sleeper so that the body motion of the sleeper can be precisely detected.