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; a first detection part that acquires a first detection result R1 by continuously or intermittently detecting a position of an edge of the base material in a width direction at a first detection position Pa in said transport path; a second detection part that acquires a second detection result R2 by continuously or intermittently detecting a position of the edge of the base material in the width direction at a second detection position Pb that is located downstream of said first detection position Pa in said transport path; and a displacement amount calculation part configured to calculate an amount of expansion and contraction Ew of the base material in the width direction on the basis of said first detection result R1 and said second detection result R2; characterized in that the displacement amount calculation part is further configured to calculate an amount of displacement in a position of the base material in a transport direction on the basis of (i) a result that is obtained by multiplying a calculation result of the amount of expansion and contraction Ew of said base material in the width direction by an aspect ratio that is a ratio k between the amount of expansion and contraction Ew of the base material in the width direction and an amount of expansion and contraction El of the base material in the transport direction or (ii) a result that is obtained by substituting a calculation result of the amount of expansion and contraction Ew of said base material in the width direction into a matrix transformation that expresses a relationship between the amount of expansion and contraction Ew of the base material in the width direction and an amount of expansion and contraction El of the base material in the transport direction. a transport mechanism that transports a long band-like base material in a longitudinal direction along a predetermined transport path; a first detection part that acquires a first detection result R1 by continuously or intermittently detecting a position of an edge of the base material in a width direction at a first detection position Pa in said transport path; a second detection part that acquires a second detection result R2 by continuously or intermittently detecting a position of the edge of the base material in the width direction at a second detection position Pb that is located downstream of said first detection position Pa in said transport path; and a displacement amount calculation part configured to calculate an amount of expansion and contraction Ew of the base material in the width direction on the basis of said first detection result R1 and said second detection result R2; characterized in that the displacement amount calculation part is further configured to calculate an amount of displacement in a position of the base material in a transport direction on the basis of (i) a result that is obtained by multiplying a calculation result of the amount of expansion and contraction Ew of said base material in the width direction by an aspect ratio that is a ratio k between the amount of expansion and contraction Ew of the base material in the width direction and an amount of expansion and contraction El of the base material in the transport direction or (ii) a result that is obtained by substituting a calculation result of the amount of expansion and contraction Ew of said base material in the width direction into a matrix transformation that expresses a relationship between the amount of expansion and contraction Ew of the base material in the width direction and an amount of expansion and contraction El of the base material in the transport direction.