The purchase, which local media put at around $870 million, was aimed at expanding the global reach of Toshiba's half-owned Toshiba Tec Corp, making it the world's largest vendor of POS systems and equipment, the source told Reuters.
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The company's board had yet to meet to finalise the deal, the source added.
Toshiba Tec shares gained 7.5 per cent in Tokyo to 329 yen, outperforming a flat overall market.
Toshiba Tec would pay 70 billion yen for the IBM business - which counts Wal-Mart and Toys "R" Us as customers - mainly financing the deal with cash reserves and bank loans, the Nikkei business daily reported.
IBM holds the top slot in the global POS terminal market with a share of 22 per cent, the Nikkei said, compared with a 7 per cent share for the Toshiba subsidiary.
IBM's technology would strengthen Toshiba's cloud computing services that enable stores, shoppers, manufacturers and others to exchange information and offer services, it said.