Japanese Finance Minister Hirohisa Fujii, 77, was admitted to hospital on Monday for tests, a ministry spokesman said.
"He has been working continuously, so it is partly to get some rest," a ministry spokesman said. Fujii has slightly high blood pressure but no other symptoms, the spokesman said.
Fujii was at the center of wrangling over the past few weeks about how to balance the heavily indebted government's budget for the fiscal year from next April 1, Reuters reported.
One sticking point in the budget, which was agreed on Friday, was how to balance keeping a limit on government bond issuance against costly pledges made by the ruling Democratic Party in the run-up to the August election that brought it to power.
Kyodo news agency said Fujii was likely to stay in hospital for about 10 days, but the spokesman said he could not confirm this.