A titanium alloy includes at least one alloying element whose molybdenum equivalent "Mo.sub.eq" is from 3 to 11% by mass, at least one interstitial solution element selected from the group consisting of O, N and C in an amount of from 0.3 to 3% by mass, and the balance of Ti, when the entirety is taken as 100% by mass. Its content of Al is controlled to 1.8% by mass or less, and it is .beta. single phase at room temperature at least.