Your code works OK for me. That's what I have run:

#!/usr/bin/perl

use strict;
use warnings;

use LWP::Parallel::UserAgent;

my $url =
"http://www.ypbooks.co.kr/ypbooks/WebHome/specdm/specdm.jsp?p_isbn=194
+1700216";

my $ua = LWP::Parallel::UserAgent->new();
   $ua->redirect (1);
   $ua->timeout  (2);
   $ua->max_hosts (3);
   $ua->max_req (3);

my $response = $ua->get( $url );

my $contents =  $response->content;

print $contents;
[download]