What was Sega's first home video-game console?

Sega's first home video-game console was the SG-1000.

Sega released the SG-1000 in Japan on July 15, 1983, the same day Nintendo launched the Family Computer there. Sega had previously developed arcade machines and electromechanical amusements, but the SG-1000 was its first dedicated home console.

The system used interchangeable cartridges and also supported a separately sold keyboard accessory called the SK-1100. Sega revised the hardware as the SG-1000 II in 1984, improving the design and adding controller features. The console was sold in several markets, though it never achieved the global prominence later associated with the Master System or Genesis.

The SG-1000 is sometimes mistakenly called Sega's first 8-bit console internationally, with the Master System receiving that description more often. Historically, however, the SG-1000 came first. Its release marked Sega's direct entry into the increasingly competitive home-console business.