The Joypad (ジョイパッド) SJ-150 is the default controller bundled with SG-1000 II consoles. It replaced the SJ-200, and copied its design from the Nintendo Famicom, sporting a D-Pad and two face buttons.
The SJ-150 would start a trend that would continue among Sega controllers (and some non-Sega ones) until the release of the Sega Mega Drive - a detachable thumbstick which can be placed within the middle of the D-Pad to create something similar to the SJ-200's joystick. Presumably because this thumbstick got in the way of gameplay, it was removed in later controllers. The design may have also been put in place to avoid legal issues with Nintendo, who had patented the familiar D-Pad cross design.
Like the Nintendo Famicom the controllers were designed to be stored on the sides of the SG-1000 II console when not in use, so the controller leads come out of the right hand side of the controller rather than the top. This can lead to some discomfort during play.