An apparatus for detecting seated condition for toilet seat which detects whether the change in input voltage of determining circuit, over predetermined time, in response to electrostatic capacity is existed or not. When the change is existed, the present apparatus computes and renews the set value 1 for detecting un-seated condition and the set value 2 for detecting seated condition based on the changed input potential.Accordingly, the present apparatus is the apparatus for detecting whether a human is seated or un-seated on a toilet seat using electrostatic capacity and the present invention can reduce the error in detection caused by the change in electrostatic capacity owing to a person, temperature and humidity.