The present invention comprises: an absorbent core which is disposed in an absorbent article and absorbs excretions a pair of conductive members which are disposed in the absorbent article and have conductivity a detection part which detects the size of impedance between the conductive members and a control part which detects the presence or absence of excretion on the basis of a change pattern over time of the impedance detected by the detection part and determines timing to change the absorbent article by comparing the size of impedance after a prescribed time has passed after excretion is detected with a prescribed threshold.