A controller comprising: a first calculator configured to receive process data and vital data, the process data being measurement data of a state quantity in an industrial process and received from a field device, the vital data being biological information of a plant worker and received from a sensor attached to the plant worker, the first calculator calculating first index data and second index data, the first index data indicating a gap between a current one of the process data and a previous one of the process data which is received when the plant is in a normal state, the second index data indicating a gap between a current one of the vital data and a previous one of the vital data which is received when the plant is in the normal state; and a first determiner configured to determine first information of the plant by using the first index data and the second index data which are calculated by the first calculator, the first information of the plant representing at least one of an abnormal state in which there is a need to stop the industrial process, an unstable state in which there is a need to reconfirm an operation performed by the plant worker, and a normal state in which there is no need to stop the process and reconfirm the operation, wherein the first calculator is configured to calculate the first index data by calculating a difference between the current one of the process data and the previous one of the process data, and to calculate the second index data by calculating a difference between the current one of the vital data and the previous one of the vital data; and the first determiner is configured to determine that the plant is in the abnormal state in a case where the first index data exceeds a first threshold value, to determine that the plant is in the unstable state in a case where the first index data does not exceed the first threshold value and the second index data exceeds a second threshold value, and to determine that the plant is in the normal state in a case where the first index data does not exceed the first threshold value and the second index data does not exceed the second threshold value. a first calculator configured to receive process data and vital data, the process data being measurement data of a state quantity in an industrial process and received from a field device, the vital data being biological information of a plant worker and received from a sensor attached to the plant worker, the first calculator calculating first index data and second index data, the first index data indicating a gap between a current one of the process data and a previous one of the process data which is received when the plant is in a normal state, the second index data indicating a gap between a current one of the vital data and a previous one of the vital data which is received when the plant is in the normal state; and a first determiner configured to determine first information of the plant by using the first index data and the second index data which are calculated by the first calculator, the first information of the plant representing at least one of an abnormal state in which there is a need to stop the industrial process, an unstable state in which there is a need to reconfirm an operation performed by the plant worker, and a normal state in which there is no need to stop the process and reconfirm the operation, wherein the first calculator is configured to calculate the first index data by calculating a difference between the current one of the process data and the previous one of the process data, and to calculate the second index data by calculating a difference between the current one of the vital data and the previous one of the vital data; and the first determiner is configured to determine that the plant is in the abnormal state in a case where the first index data exceeds a first threshold value, to determine that the plant is in the unstable state in a case where the first index data does not exceed the first threshold value and the second index data exceeds a second threshold value, and to determine that the plant is in the normal state in a case where the first index data does not exceed the first threshold value and the second index data does not exceed the second threshold value.