A diagnosis apparatus includes a fiber optic sensor, a collection processor, and a self-diagnosis processor. The fiber optic sensor is configured to be disposed over a target. The collection processor is configured to perform a collection process that collects measurement data related to the target obtained by the fiber optic sensor. The self-diagnosis processor is configured to perform a self-diagnosis process before the collection processor starts the collection process. The self-diagnosis process obtains an output value related to calibration of the fiber optic sensor, causes the collection processor to start the collection process when the output value falls within a proper range, and outputs an error when the output value falls outside the proper range.