T-Mar

That's exactly what I was expecting. It's a 1982 model manufactured by Miki of Japan. Their quasi-aero frames are distinctive due the aero down and seat tubes being round at the BB end. They also attached the brake cable tunnels under the top tube. I've always considered Miki's quasi-aero approach to be quite intelligent. It allows for a standard, clamp style front derailleur and BB shell, both which save costs. The air flow is very disturbed around the BB shell, so the aerodynamics are not as importnat in this area.

Miki was a contract manufacturer and built for several companies. I've seen this exact frame under a few different brand names, so it's appears to be a stock Miki offering. Here's an SR Semi-Pro owned by member Cliffordk with the same frame characteristics. It's perhaps the most popular brand that used these Miki frames, so it would be my leading candidate. The non-drive side photo better shows the transition of the down and seat tubes form aero profile to round as they approach the BB shell.