To provide a seal inspection method, a seal inspection device, and a diagnostic method for packing/filling machines which improve precision of an inspection result by the seal inspection device (method), can be used for condition management of a packing/filling machine, can discover a defective state of the filling-up machine caused by its variations with time at an early stage, grasp each operating condition at real time, enable the adjustment of parameters of the filling-up machine and estimation of time for its component exchanges, and prevent occurrence of defective units.

Seal inspection and diagnosis of the packing/filling machine comprise loading a preknown pressure to the inside of a vessel obtained by sealing a web-like packing laminated material and applying a pressure to a sealed zone, performing seal inspection, comparing a result value of the seal inspection and a standard seal inspected value and diagnosing the packing/filling machine.