A method for verifying mask pattern data includes preparing design circuit data on a design circuit which realizes a desired electrical operation. Data on a design circuit pattern having a structure which realizes the design circuit on a semiconductor substrate is prepared. Mask pattern data on a pattern of a mask used in order to produce the design circuit pattern is prepared. A circuit pattern which is to be obtained by processing a film using the pattern of the mask indicated by the mask pattern data is acquired. Circuit data on a circuit realized by at least a first part of the circuit pattern is produced. A circuit mismatch part where the circuit data and a part of the design circuit data which corresponds to the first part of the circuit pattern do not match up is detected.