Update : Jan. 04, 2010
As mentioned in 'What kind of market information is available to investors?', investors are keenly interested in the state of the order book before the opening price is determined. So TSE provides pre-opening quotes in the period prior to the opening auctions (from 08:20 for the morning session, and from 12:05 for the afternoon session). This quote is an estimate of the expected opening price, and only indicates a probability. It is the price at which offers and bids are currently offered.
The following table illustrates the order book prior to the start of trading. As you can see the aggregated offers and bids balance out at 500 yen and 499 yen respectively. So TSE indicates a bid of 500 shares at 499 yen and an offer of 600 shares at 500 yen . This shows investors that the opening price is likely to be either 499 yen or 500 yen . TSE also provide the 7 next best buy and sell prices along with their number of shares.
As mentioned in 'What kind of market information is available to investors?, orders continue to be placed into the trading system right up until the opening auction, so the pre-opening price will change to reflect the altered balance of the order book. Thus, the pre-opening quotes indicated at 08:30 and 08:55 could very well be different. Investors must therefore keep a careful eye on this quote, so as not to be misled.