A surface inspection apparatus includes a blocking unit included in a subsequent processing unit that groups data items into having an arbitrary number of data items. The subsequent processing unit acquires a data item from each of the blocks. The blocking unit changes, in accordance with an instruction transmitted from a state monitoring unit, the number of data items to be blocked. A threshold processing unit acquires data items from the blocking unit that have values larger than a threshold, and transmits the data items to a memory. The state monitoring unit monitors an available capacity of the memory. When the state monitoring unit detects a reduction in the available capacity of the memory, it causes the blocking unit to increase the number of data items to be blocked into each of the blocks so that data does not overflow from the memory.