A condition monitoring system that diagnoses an abnormality of an apparatus provided in a wind turbine comprising: a monitoring apparatus including a plurality of sensors (70A-70H) for measuring a measurement data indicating the state of said apparatus and operating condition data indicating the operating condition of said wind turbine, said monitoring apparatus calculating the diagnostic parameter from the measured data; a monitoring-side control apparatus that sets a first threshold value to be used by said monitoring apparatus for diagnosing the abnormality of said apparatus, and diagnoses the abnormality of said apparatus based on said threshold value, said monitoring-side control apparatus including a storage unit that stores information; and a monitoring terminal apparatus that monitors a condition of said apparatus,said monitoring terminal apparatus including a display unit for displaying information, said monitoring-side control apparatus being coupled with each of said monitoring apparatus and said monitoring terminal apparatus by a communication channel, said monitoring terminal device sequentially setting a first time period for collecting basic data, a second period for setting said first threshold value and a third period for diagnosing the abnormality of said apparatus, in said first period, the measurement data measured and calculated by said monitoring apparatus, the operating condition data, and the diagnostic parameter are stored in said storage unit and displayed on said display unit and a diagnosis operation condition being set by using said monitoring terminal apparatus, in said second period, when the operating condition of said wind turbine satisfies said diagnostic operation condition, the diagnostic parameter calculated from the measured measurement data being stored in said storage unit and said monitoring-side control apparatus generating said first threshold value based on the diagnostic parameter stored in said storage unit, in said third period, when the operating condition of said wind turbine satisfies said diagnostic operation condition, the diagnostic parameter calculated from the measured measurement data being stored in the storage unit and said monitoring-side control apparatus comparing said first threshold value with the diagnostic parameter stored in said storage unit, and if the diagnostic parameter is greater than said first threshold value, it is determined that an abnormality has occurred in said apparatus and the determined result is stored in the storage unit and displayed on the display unit. a monitoring apparatus including a plurality of sensors (70A-70H) for measuring a measurement data indicating the state of said apparatus and operating condition data indicating the operating condition of said wind turbine, said monitoring apparatus calculating the diagnostic parameter from the measured data; a monitoring-side control apparatus that sets a first threshold value to be used by said monitoring apparatus for diagnosing the abnormality of said apparatus, and diagnoses the abnormality of said apparatus based on said threshold value, said monitoring-side control apparatus including a storage unit that stores information; and a monitoring terminal apparatus that monitors a condition of said apparatus,said monitoring terminal apparatus including a display unit for displaying information, said monitoring-side control apparatus being coupled with each of said monitoring apparatus and said monitoring terminal apparatus by a communication channel, said monitoring terminal device sequentially setting a first time period for collecting basic data, a second period for setting said first threshold value and a third period for diagnosing the abnormality of said apparatus, in said first period, the measurement data measured and calculated by said monitoring apparatus, the operating condition data, and the diagnostic parameter are stored in said storage unit and displayed on said display unit and a diagnosis operation condition being set by using said monitoring terminal apparatus, in said second period, when the operating condition of said wind turbine satisfies said diagnostic operation condition, the diagnostic parameter calculated from the measured measurement data being stored in said storage unit and said monitoring-side control apparatus generating said first threshold value based on the diagnostic parameter stored in said storage unit, in said third period, when the operating condition of said wind turbine satisfies said diagnostic operation condition, the diagnostic parameter calculated from the measured measurement data being stored in the storage unit and said monitoring-side control apparatus comparing said first threshold value with the diagnostic parameter stored in said storage unit, and if the diagnostic parameter is greater than said first threshold value, it is determined that an abnormality has occurred in said apparatus and the determined result is stored in the storage unit and displayed on the display unit.