A parallel processing apparatus includes, a plurality of operational circuits that execute operations for data in parallel, and a control circuit that, upon an end of operations for a first portion of the data, finds estimated operation time for operations for a second portion that is an object of operations subsequent to the first portion, based on target time for operational processing for the data and a data amount of remaining data for which no operation has been executed in the data, finds a second parallelism of the operations for the second portion, based on a first parallelism of the operations for the first portion, a measurement value of operation time for the operations for the first portion, and the estimated operation time, and causes operational circuits, numbering in a number indicated by the second parallelism among the plurality of operational circuits, to execute the operations for the second portion.