Sa Aung Myo Myat, 21, found the abandoned cassette player on Friday on top of a car outside a shop in Pha-An, the capital of Kayin state, also known as Karen state, bordering Thailand.
"It exploded when he pressed its button out of curiosity," the state-owned Myanma Ahlin newspaper said on Saturday.
Three other students - Maung Aung Soe Moe, Maung Chit Nyi, and Maung Win Phone Kyaw - were wounded in the blast.
"The authorities concerned are making investigations to expose the destructive bombers," the newspaper said.
"The general public has also been warned and urged to inform the authorities if any unattended suspicious packages, radios, cassette players or watches are found," it added.
It was the second bomb attack in Myanmar this week after a blast in a Yangon restaurant killed one employee on Tuesday.
Authorities are hunting for two men who witnesses said left a package inside the restaurant before the blast.
The military, which has ruled Myanmar in various guises since 1962, has blamed previous attacks on "destructive elements" - an expression often used to refer to political opponents and ethnic minority rebel groups fighting for autonomy.
The party of Myanmar democracy icon Aung San Suu Kyi, who is under house arrest at her Yangon home, has condemned Tuesday's Yangon bombing as a "terrorist act".
"As the National League for Democracy is working through peaceful means for the emergence of a democracy and human rights in this country, we cannot accept this kind of act," the party said in a statement on Friday.