Tsunoda was (maybe still is?) a Japanese manufacturer. Tsunoda did a lot of contract builds, manufacturing bicycles for other brands like Lotus. Very much like how Kawamura manufactured Nishiki frames or how Panasonic built frames for Schwinn.

Judging by features like the stamped dropouts, cottered cranks, and 'safety levers', your particular bike is an entry-level model. The SunTour components are circa 1970s, so that puts it squarely in the "bike boom" era.

As far as cheap '70s bikes go, it looks to be in great shape and those SunTour parts worked well, so it should be a satisfactory rider even if it's on the heavy side. Because of the bike's age, you'd definitely want to give it a once-over to do things like service bearings and replace consumables that might've degraded with age like brake pads.