installing Sqlite3-ruby error

Question

When I tried to install: gem install sqlite3-ruby it shows:

    Building native extensions.  This could take a while...
ERROR:  Error installing sqlite3-ruby:
    ERROR: Failed to build gem native extension.

/usr/bin/ruby1.8 extconf.rb
extconf.rb:3:in `require': no such file to load -- mkmf (LoadError)
    from extconf.rb:3


Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.3.1 for inspection.
Results logged to /usr/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.3.1/ext/sqlite3/gem_make.out

My environment: sqlite: 2.8.17 rails: 3.0.0 ruby: 1.9.2 ubuntu: 10.04 gem: 1.3.7

I have looking all similiar question in webs and SO, nothing help, what should I do? :(