Google Lotus road bike. Lotus bikes are no different than many other Japanese bike boom bikes in that they had a range of quality. I would say from what I've seen, even the lower end is very nice. I was in Evansville Indiana on business recently and stopped in a bike shop there. One of the employees had his bike in the back and offered to show it to me. It was a Lotus and had Tange Infinity tubing and Shimano 600 components. It was very nice indeed.

Post a picture so that we can see it. If it is late '70s there is a good chance that it will have Suntour components. When we know what model of component we can nail it down further, or you can look up the serial number on Velobase.com and check out the vintage there.