can i decrease the query time?

i created index already. how can i decrease the query time more.

number of record is over 1 million.
the following is the query plan. 

Group (cost=34082.59..34085.62 rows=61 width=112)
-> Sort (cost=34082.59..34082.59 rows=607 width=112)
-> Nested Loop (cost=0.00..34054.51 rows=607 width=112)
-> Nested Loop (cost=0.00..125.64 rows=2 width=108)
-> Nested Loop (cost=0.00..8.84 rows=1 width=22)
-> Index Scan using tbl_member_pkey on tbl_member d (cost=0.00..5.14
rows=1 width=18)
-> Index Scan using tbl_company_pkey on tbl_company c (cost=0.00..3.68
rows=1 width=4)
-> Index Scan using tbl_adpage_pkey on tbl_adpage b (cost=0.00..112.65
rows=332 width=86)
-> Index Scan using tbl_showlog_adpage_id_idx on tbl_showlog a
(cost=0.00..20370.75 rows=5466 width=4)