Elon Musk bought $10 million of shares in Tesla Inc. on Monday and plans to spend another $20 million on stock in the company, according to the company.

The chief executive of the electric-vehicle company bought close to 30,000 Tesla shares in three separate transactions, Tesla said in a filing posted on its website Tuesday. Using a trust, Mr. Musk paid between an average of $334.24 a share and $335.93 a share in the transactions.