Thank you all for your suggestions. I summarized books mentioned so far, including that are not only recommended but also unread by anyone or yet published, but excluding that about individual composers, with rough coverage. Forgive me for any mistakes, I tried to get information from web sites for those books I don't have.
Music in the Early Twentieth Century: The Oxford History of Western Music by Richard Taruskin
Music in the Late Twentieth Century: The Oxford History of Western Music by Richard Taruskin
A Concise History of Modern Music by Paul Griffiths : Debussy ~ Boulez (1978)
The Rest Is Noise by Alex Ross : Mahler ~ Bjork (?)
Music in the Twentieth and Twenty-First Centuries by Joseph Auner : Mahler ~ Chen Yi (?)
The Companion To 20th-century Music by Norman Lebrecht : 1900 ~ 1996
New Music at Darmstadt: Nono, Stockhausen, Cage, and Boulez (Music Since 1900) by Dr Martin Iddon
The Music of William Schuman, Vincent Persichetti, and Peter Mennin: Voices of Stone and Steel by Walter Simmons
The New Music: The Avant-garde since 1945 by Reginald Smith Brindle : 1945 ~ 1986
Modern Music - The avant garde since 1945 by Paul Griffiths : 1945 ~ 1981
Modern Music and After by Paul Griffiths : 1945 ~ 21th Century (Lachenman, Sciarrino, )
Experimental Music by Michael Nyman : 1950 ~ 1970, Cage, Cardew, Boulez, Berio, Stockhausen
American Music in the Twentieth Century by Kyle Gann : Ives ~ 1990s
The New York Schools of Music and the Visual Arts by Steven Johnson : 1st half of 20th Century (Cage, Feldman, Brown, Tudor)
This Life of Sounds: Evenings for New Music in Buffalo by Renee Levine Packer : 1964 ~ 1980, new music in America
Music Downtown: Writings from the Village Voice by Kyle Gann : 1980 ~ 1990s, Music in NYC
Electronic & Computer Music by Peter Manning : 1945 ~ present
"a history of modern composition since 1989" by Tim Rutherford-Johnson (not published) : 1989 ~ present?
[EDIT] Corrected mistakes; Added Taruskin books.