A process monitoring system comprising: a first field device configured to measure a first state quantity in an industrial process implemented in a plant; a second field device configured to measure a second state quantity in the industrial process; a trend calculation unit configured to determine a first variation trend of the first state quantity, based on first time-sequence data output from the first field device, determine a second variation trend of the second state quantity, based on second time-sequence data output from the second field device, classify, at a time, the first variation trend into a first status among a pre-established plurality of statuses, the first status indicating that the first variation trend has a positive slope, an approximately zero slope, or a negative slope, and classify, at the time, the second variation trend into a second status among the pre-established plurality of statuses, the second status indicating that the second variation trend has a positive slope, an approximately zero slope, or a negative slope; and a state change judgment unit configured to judge whether a plant state of the plant is healthy or not based on the first status and the second status, the judgment being made by using a pre-established relationship between the first status, the second status and the plant state; and a notification unit configured to notify of a judgment result of the state change judgment unit. a first field device configured to measure a first state quantity in an industrial process implemented in a plant; a second field device configured to measure a second state quantity in the industrial process; a trend calculation unit configured to determine a first variation trend of the first state quantity, based on first time-sequence data output from the first field device, determine a second variation trend of the second state quantity, based on second time-sequence data output from the second field device, classify, at a time, the first variation trend into a first status among a pre-established plurality of statuses, the first status indicating that the first variation trend has a positive slope, an approximately zero slope, or a negative slope, and classify, at the time, the second variation trend into a second status among the pre-established plurality of statuses, the second status indicating that the second variation trend has a positive slope, an approximately zero slope, or a negative slope; and determine a first variation trend of the first state quantity, based on first time-sequence data output from the first field device, determine a second variation trend of the second state quantity, based on second time-sequence data output from the second field device, classify, at a time, the first variation trend into a first status among a pre-established plurality of statuses, the first status indicating that the first variation trend has a positive slope, an approximately zero slope, or a negative slope, and classify, at the time, the second variation trend into a second status among the pre-established plurality of statuses, the second status indicating that the second variation trend has a positive slope, an approximately zero slope, or a negative slope; and a state change judgment unit configured to judge whether a plant state of the plant is healthy or not based on the first status and the second status, the judgment being made by using a pre-established relationship between the first status, the second status and the plant state; and a notification unit configured to notify of a judgment result of the state change judgment unit.