Patent ID: 8856888

Claim:
A personal authentication apparatus that controls an authenticated state of a target device based on motion of the target device, the apparatus comprising: a motion sensor that detects motion information indicating the motion of the target device; and a processor executing instructions implementing: a carried-state determination unit configured to determine whether or not the target device is being carried by a user based on the detected motion information; a degree-of-confidence determination unit configured to determine a degree of confidence that indicates a level of certainty that the target device is being carried by an authenticated user based on a result of the determination by the carried-state determination unit; and an authentication control unit configured to control the authenticated state of the target device based on the determined degree of confidence, wherein the degree-of-confidence determination unit is configured to: repeatedly make the determination of the degree of confidence over time determine a value that is smaller than a previously determined degree of confidence by a first predetermined value as a current degree of confidence, when the carried-state determination unit determines that the target device is being carried by the user; and determine a value that is smaller than the previously determined degree of confidence by a second predetermined value that is greater than the first predetermined value as the current degree of confidence, when the carried-state determination unit determines that the target device is not being carried by the user.