(Adds details on investors, background)
* Biggest approved project was for Toyota Motor
* Another involves China's SAIC and Thailand's CP
* Junta leader Gen. Prayuth chaired investment board meeting
BANGKOK, June 18 (Reuters) - Thailand's investment agency said on Wednesday it approved applications for 18 projects worth about 120 billion baht ($3.7 billion), mainly in the auto industry, at its first board meeting after the May 22 military coup.
The largest approval was for Toyota Motor Corp., which plans to spend 51.5 billion baht for production of pickup trucks and parts, the Board of Investment (BOI) said in a statement.
Wednesday's meeting was chaired by the junta's leader, Gen. Prayuth Chan-ocha.
Also approved were a tyre production project worth 18.9 billion baht by LLIT (Thailand) and production of coated steel sheets worth 10 billion baht by Posco Coated Steel (Thailand), the BOI said.
Another approved plan was for investment of 9.2 billion baht by a joint venture of SAIC Motor Corp. of China and Thailand's Charoen Pokphand Group, for car production.
Thailand is a regional vehicle production and export base for the world's top car manufacturers. Domestic auto sales in Thailand tumbled 38 percent in May from a year earlier, the Federation of Thai Industries said on Wednesday.
One approved plan, from Luxemburg's Supernap International SA's, is for a 6.9 billion baht investment in a data centre.
The projects endorsed on Wednesday are among big applications awaiting approval. The military government said early this month that backlogged applications for local and foreign investors to invest more than $21 billion would be acted on within two months.
The army seized power in a bid to restore order and business confidence after months of political unrest hurt consumption and investment.
The total value of investment applications fell 42 percent to 308 billion baht in the first five months of this year from a year earlier. Within that, foreign investment requests dropped 10 percent to 230 billion baht.
The junta has announced measures it hopes will get the sputtering economy going again. It is seeking to fast-track infrastructure spending, which has been derailed by the political crisis.
On Wednesday, Thailand's central bank cut this year's growth forecast nearly by half to 1.5 percent but it saw a much brighter 2015 as the military government tries to reinvigorate the economy. (Reporting by Orathai Sriring and Viparat Jantraprap; Editing by Richard Borsuk)