The invention relates to a field device which is capable of diagnosing a wide range of possible errors and/or conditions. Said device comprises a unit for carrying out user-specific diagnostic methods (25), which unit comprises an input circuit (27) via which at least one input variable (E) is supplied to the unit, an evaluation unit (29) for deriving at least one parameter (Kx), using a least one user-selected input variable (Ex) and at least one user-selected evaluation method (AVx), a monitoring unit (37) that monitors the derived parameters (Kx) using the user-selected monitoring criteria (UKx), and an output unit (43) which outputs a diagnosis (Dx) associated with a monitoring criterion (UKx) when said monitoring criterion (UKx) occurs. The device further comprises an interface (47) via which a user selects the input variables (Ex) for every user-defined diagnostic method, the evaluation methods (AVx) to be applied to the input variables (Ex), the monitoring criteria (UKx), and via which the user presets the diagnosis (Dx).