TOKYO, Feb 16 (Reuters) - Industrial robot maker Fanuc Corp said on Monday it was doubling its planned investment in a new plant to 100 billion yen ($844 million), a week after activist hedge fund Third Point called on the Japanese firm to buy back more shares.

Fanuc, one of the largest industrial robot makers in the world and well known for a reluctance to use its huge cash pile for big acquisitions or buybacks, said in a statement that it will use the money to purchase land and build the plant in Tochigi prefecture, central Japan.

The company, in the statement, did not provide reasons why it decided to increase spending or whether it was related to Third Point's recent demand to buy back more shares. Fanuc did not return a telephone call seeking comment.

Third Point told investors last week that it bought a stake in Fanuc to "rerate significantly" its buyback programme, criticising its "illogical capital structure." The U.S. hedge fund was not immediately available to comment for this article.

Fanuc regularly manages a return on equity that exceeds the industry average, but analysts have said it could return even more considering its EBITDA margin is 41 percent compared with around 11 percent among its peers. EBITDA refers to earnings before interest, tax, depreciation and amortisation.

The company also has no debt and ended its last fiscal year with cash and equivalents of 823.7 billion yen.

Fanuc initially announced the new plant in September. The plant will make equipment such as computer numerical control (CNC) systems beginning in October, 2016.

Fanuc also said on Monday it plans to spend an additional 30 billion yen to expand laboratories at its headquarters in Yamanashi prefecture.

Fanuc shares were 3.5 percent higher at 22,410 yen in early afternoon trade, compared with a 0.5 percent rise in the Nikkei average. ($1 = 118.5300 yen) (Reporting by Ritsuko Ando; Editing by Christopher Cushing)