Abase material processing apparatus comprising: a transport mechanism that transports a long band-like base material in a longitudinal direction along a predetermined transport path; an upstream detector that successively or intermittently detects a position of an edge of the base material in a width direction at an upstream detection position (Pa) in the transport path to acquire an upstream detection result (R1); and a downstream detector that successively or intermittently detects the position of the edge of the base material in the width direction at a downstream detection position (Pb) located downstream of the upstream detection position (Pa) in the transport path to acquire a downstream detection result (R2); characterized in that the base material processing apparatus further comprises a displacement amount calculation part that, for each upstream data section (D1) that is a data section included in the upstream detection result (R1), is configured to identify a highly matched downstream data section (D2) from among a plurality of downstream data sections that are data sections included in the downstream detection result (R2), and is configured to calculate an amount of displacement of the base material in a transport direction or an amount of difference in a transport speed of the base material on the basis of an identification result, wherein the displacement amount calculation part is configured to use a result of comparison between signals in a predetermined frequency band extracted from the upstream detection result (R1) and signals in the predetermined frequency band extracted from the downstream detection result (R2) to identify the highly matched downstream data section (D2) for each of the upstream data sections. a transport mechanism that transports a long band-like base material in a longitudinal direction along a predetermined transport path; an upstream detector that successively or intermittently detects a position of an edge of the base material in a width direction at an upstream detection position (Pa) in the transport path to acquire an upstream detection result (R1); and a downstream detector that successively or intermittently detects the position of the edge of the base material in the width direction at a downstream detection position (Pb) located downstream of the upstream detection position (Pa) in the transport path to acquire a downstream detection result (R2); characterized in that the base material processing apparatus further comprises a displacement amount calculation part that, for each upstream data section (D1) that is a data section included in the upstream detection result (R1), is configured to identify a highly matched downstream data section (D2) from among a plurality of downstream data sections that are data sections included in the downstream detection result (R2), and is configured to calculate an amount of displacement of the base material in a transport direction or an amount of difference in a transport speed of the base material on the basis of an identification result, wherein the displacement amount calculation part is configured to use a result of comparison between signals in a predetermined frequency band extracted from the upstream detection result (R1) and signals in the predetermined frequency band extracted from the downstream detection result (R2) to identify the highly matched downstream data section (D2) for each of the upstream data sections. <EOS>