diff --git a/lib/ipaddr.rb b/lib/ipaddr.rb
index 59427bc..898af26 100644
--- a/lib/ipaddr.rb
+++ b/lib/ipaddr.rb
@@ -205,6 +205,30 @@ def to_i
     return @addr
   end
 
+  # Returns a string containing the binary representation of the
+  # IP address value, right adjusted to the address size (32 bits
+  # for IPv4, 128 bits for IPv6), regardless of the prefix length.
+  #
+  # e.g.:
+  #   require 'ipaddr'
+  #   p IPAddr.new("192.168.1.1").to_bits
+  #   #=> "11000000101010000000000100000001"
+  #   p IPAddr.new("3ffe:505:2::1").to_bits
+  #   #=> "00111111111111100000010100000101" \
+  #   #   "00000000000000100000000000000000" \
+  #   #   "00000000000000000000000000000000" \
+  #   #   "00000000000000000000000000000001"
+  def to_bits
+    case @family
+    when Socket::AF_INET
+      @addr.to_s(2).rjust(32, '0')
+    when Socket::AF_INET6
+      @addr.to_s(2).rjust(128, '0')
+    else
+      raise AddressFamilyError, "unsupported address family"
+    end
+  end
+
   # Returns a string containing the hexadecimal representation of the
   # IP address value, right adjusted to the address size.
   #
diff --git a/test/test_ipaddr.rb b/test/test_ipaddr.rb
index 6af7b73..daa68e6 100644
--- a/test/test_ipaddr.rb
+++ b/test/test_ipaddr.rb
@@ -304,6 +304,23 @@ def test_to_s_with_zone_id
     assert_equal("fe80::1%0012", IPAddr.new("fe80::1%0012").to_s)
   end
 
+  def test_to_bits
+    assert_equal("11000000101010000000000100000001", IPAddr.new("192.168.1.1").to_bits)
+    assert_equal("00000000000000000000000000000000", IPAddr.new("0.0.0.0").to_bits)
+    assert_equal("00111111111111100000010100000101" + "00000000000000100000000000000000" +
+                 "00000000000000000000000000000000" + "00000000000000000000000000000001",
+                 IPAddr.new("3ffe:505:2::1").to_bits)
+    assert_equal("00000001001000110100010101100111" + "10001001101010111100110111101111" +
+                 "00001010101111001101111011110000" + "00010010001101000101011001111000",
+                 IPAddr.new("123:4567:89ab:cdef:0abc:def0:1234:5678").to_bits)
+    assert_equal("00000000000000000000000000000000" + "00000000000000000000000000000000" +
+                 "00000000000000000000000000000000" + "00000000000000000000000000000000",
+                 IPAddr.new("::").to_bits)
+    assert_equal("11111111111111111111111111111111" + "11111111111111111111111111111111" +
+                 "11111111111111111111111111111111" + "11111111111111111111111111111111",
+                 IPAddr.new("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff").to_bits)
+  end
+
   def test_to_hex
     assert_equal("c0a80101", IPAddr.new("192.168.1.1").to_hex)
     assert_equal("00000000", IPAddr.new("0.0.0.0").to_hex)