According to one embodiment, a program converting device includes an access attribute determining unit, a non-sharing target classifying unit, and a converting unit. The access attribute determining unit calculates exclusive accesses from memory accesses by threads forming a source program and determines a memory access using a cache memory among the calculated exclusive accesses. The non-sharing target classifying unit determines an access data item that does not share a cache line with another access data item among the access data items that are accessed using the cache memories. The converting unit inserts a process that does not share the cache line into the source program based on the determination result of the non-sharing target classifying unit.