PURPOSE: To conduct more stable feed control in a sheet material processing apparatus.

CONSTITUTION: Patterns of upper and lower sheet materials 10, 12 fed by upper and lower feed dogs 4, 6 are respectively detected to calculate a pattern shifting amount (d) according to a preset pattern shifting amount calculating mode (S200) and calculate the amount (dd) of change of pattern shifting amount (S210). Subsequently, according to this pattern shifting amount (d), amount (dd) of change of pattern shibting amount and a pattern overlapping state (h), address operation for inputting a controlled variable from a table of controlled variables is performed, and according to the address obtained by this address operation, a controlled variable is read out (S220). According to the input controlled variable, the walking is controlled (S230). Thus, walking is controlled to control the relative feed between upper and lower sheet materials 10, 12, so that the upper and lower sheet materials 10, 12 are sewen without uneven material feeding and with the patterns of both materials matched.