Cause estimation device, cause estimation system, and program

The purpose of the present invention is to provide more useful information to a user by specifying an estimation cause and countermeasure that takes into account a poor reliability of sensor information. This cause estimation device is provided with: a communication unit that acquires failure mode information indicating a failure mode occurring in a device or a product, an observed value of the device, and sensor information indicating a state of the device; a storage unit that stores cause estimation information in which a defect pattern, an observation value, an observation item indicating the state of the device, and a prescribed estimation cause and countermeasure are registered in association with each other; and a cause estimation unit that specifies a prescribed estimated cause and countermeasure from the cause estimation information on the basis of information acquired from an external device, wherein the cause estimation unit specifies the reliability of the sensor information using a prescribed thre