Abstract:
A game machine capable of providing proper expected values. 
     The game machine is provided with a prize decision table to be applied to a game in an ordinary probability game state and a prize decision table to be applied to a game in a high probability game state. The former and latter prize decision tables are stored with at least data of numbers of lottery random numbers for providing basis of the individual lottery probabilities for individual prize modes. By increasing the number of lottery random numbers for a predetermined mode in the high probability game state but by decreasing the number of lottery random numbers for another mode, the prize probability of the predetermined mode is enhanced, and an expected value to be obtained in the high probability game state is set to a proper expected value or less.

Description:
This patent application claims priority based on the Japanese patent application, H10-64820 filed on Feb. 27, 1998 the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a game machine having a variety of prize modes and, more particularly, to a game machine having a function to make a change to a game state, in which a predetermined prize mode is easily concentrated, when a predetermined condition is satisfied. 
     2. Related Art 
     Conventionally, the game machine equipped with such various prize modes is prepared to have a plurality of prize modes of low bonuses (as will be called the “low bonus modes”) and a plurality of prize modes of high bonuses (as will be called the “high bonus modes”) so that any of these low bonus modes and high bonus modes may be selected by a random number lottery. 
     For each prize mode, on the other hand, the lottery probabilities and the bonus numbers are predetermined according to the bet numbers so that the game can be played within a range of the expected value which is determined by those bet number, lottery probability and bonus number. Here, the expected value indicates how many coins can be expected for each coin inserted for a game. 
     There are further prepared a game state set to a relatively low expected value R L  (as will be called the “ordinary probability game state”) and a game state set to a higher expected value R H  than that of the ordinary probability game state (as will be called the “high probability game state”). If a predetermined condition is satisfied during in a play in the ordinary probability game state, the game state is changed to the high probability game state so that a predetermined prize mode is concentratively prized to give the high expected value R H  to the player. 
     For example, the conventional slot machine is prepared to have the prize modes which are called a big bonus game (as will be called the “BB game”), a regular bonus game (as will be called the “RB game”) and a single bonus game (as will be called “SB game”) as the high bonus modes, and a small mode such as “Replay”, “Bell” or “Bullet” as the low bonus modes. 
     On the other hand, there are prepared a prize decision table for the ordinary probability game state, which is stored with data of lottery probabilities a   1   to a   6   and bonus coin numbers M   1   to M   6   assigned to the respective prize modes, as shown in FIG. 1A, and a prize decision table for the high probability game state, which is stored with data of the lottery probabilities a   1   , a   2   , a   3   , a   4   to a   6   and the bonus coin numbers M   1   to M   6   assigned to the respective prize modes, as shown in FIG.  1 B. The expected value R L  in the ordinary probability game state and the expected value R H  in the high probability game state are determined on the basis of the following Formulas (1) and (2): 
     
       
         R L ={(a   1   ×M   1   )+(a   2   ×M   2   )+(a   3   ×M   3   )+(a   4   ×M   4   )+(a   5   ×M   5   )+(a   6   ×M   6   )}÷T  (1); 
       
     
     and 
     
       
         R H ={(a   1   ×M   1   )+(a   2   ×M   2   )+(a   3   ×M   3   )+(a   4   ×M   4   )+(a   5   ×M   5   )+(a6×M   6   )}÷T  (2); 
       
     
     Here in Formulas (1) and (2): T indicates the bet number; a   1   to a   6   and A   3   indicate the lottery probabilities for the respective prize modes; and M   1   to M   6   indicate the bonus coin numbers for the respective prize modes. For the “SB game”, on the other hand, the lottery probability a   3   in the ordinary probability game state and the lottery probability A   3   in the high probability game state are set in a relation of A   3   =10×a   3   , from which the expected values R L  and R H  are related to R L &lt;R H . 
     During a game in the ordinary probability game state, the random number lottery for a prize mode is performed on the basis of the prize decision table shown in FIG.  1 A. 
     If a predetermined condition is satisfied during a game in the ordinary probability game state, on the other hand, the high probability game state is established by making a change to the prize decision table, as shown in FIG.  1 B. As a result, the probability, at which the “SB game” is randomly lotted, i.e., the lottery probability is raised from a3 to A   3   (=10×a   3   ) so that the “SB game” is concentratively won to provide a game of the high expected value R H  for the player. 
     In the conventional game machine thus far described, the expected value R H  in the high probability game state is enhanced by raising only the lottery probability for a specific prize mode such as the aforementioned “SB game” when the game state is switched from the ordinary probability one to the high probability one. In the respective prize decision tables shown in FIGS. 1A and 1B, more specifically, the expected value is enhanced from R L  to R H  merely by raising the lottery probability for the “SB game” from a   3   to A   3 .    
     If the expected values R L  and R H  are set by those means, however, the expected value R H  in the high probability game state may exceed a predetermined proper expected value Rmax (e.g., 0.9) to raise the so-called “payout ratio” so excessively that no proper game mode cannot be provided for the player thereby to impose a heavy economical burden on the game house. 
     SUMMARY OF THE INVENTION 
     The invention has been conceived to solve the aforementioned problems of the related art and has an object to provide a game machine which is provided with prize decision tables capable of setting proper expected values for an ordinary probability game state and a high probability game state. 
     In order to achieve this object, according to the invention, a game machine having a plurality of prize modes and adapted to be transferred, when a predetermined condition is satisfied, from an ordinary game state to a high probability game state in which the prize probability of a predetermined one of the plurality of prize modes is enhanced, wherein the prize probability of at least one other than the predetermined prize mode in the high probability game state is set lower than the prize probability in the ordinary game state. 
     There is further provided a game machine, wherein the plurality of prize modes are lotted by a random sampling so that the prize probability of a predetermined prize mode in the high probability game state is enhanced by increasing the number of the lottery random numbers for the predetermined prize mode whereas the prize probability of the one other than the predetermined prize mode in the high probability game state is lessened by reducing the number of the lottery random numbers for the one other than the predetermined prize mode. 
     With this construction, the expected value in the high probability game state is set by raising the prize probability of a specific prize mode and by lowering the prize probability of another prize mode. As a result, it is possible to set a more proper expected value within a range at or lower than a predetermined proper expected value than to set the expected value in the high probability game state by enhancing only the prize probability for the specific prize mode. As a result, the problem that the so-called “payout ratio” becomes excessively high can be avoided in advance to provide a proper game mode for a player and to realize a game machine which will impose no economical burden on the game house or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are diagrams conceptionally showing construction of prize decision tables belonging to a conventional game machine; 
     FIG. 2 is a perspective view showing an external structure of a slot machine according to an embodiment of the invention; 
     FIGS. 3A,  3 B and  3 C are diagrams showing states in which prize lines illustrated in the display window of the slot machine shown in FIG. 2 are sequentially effected; 
     FIG. 4 is an explanatory diagram showing symbols which are illustrated on the reels of the slot machine shown in FIG. 2; 
     FIG. 5 is a diagram showing a symbol combination table which is illustrated in the prize display unit of the slot machine shown in FIG. 2; 
     FIGS. 6A,  6 B and  6 C are diagrams conceptionally showing the constructions of prize decision tables belonging to the slot machine shown in FIG. 2; 
     FIG. 7 is a block diagram showing the constructions of a control unit for controlling the operations of the slot machine shown in FIG.  2  and peripheral units; 
     FIG. 8 is a flow chart showing the game processing routine of the control unit shown in FIG. 7; 
     FIG. 9 is a flow chart further showing the game processing routine of the control unit shown in FIG. 7; 
     FIG. 10 is a flow chart showing a prize deciding routine by the control unit shown in FIG. 7; 
     FIG. 11 is a flow chart further showing the prize deciding routine by the control unit shown in FIG. 7; 
     FIG. 12 is a flow chart further showing the prize deciding routine by the control unit shown in FIG. 7; 
     FIG. 13 is a flow chart showing a BB game processing routine by the control unit shown in FIG. 7; 
     FIG. 14 is a flow chart showing an RB game processing routine by the control unit shown in FIG. 7; 
     FIG. 15 is a flow chart showing an SB game processing routine by the control unit shown in FIG. 7; and 
     FIG. 16 is a schematic diagram of a prize decision table. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Here will be described an embodiment in which a game machine of the invention is applied to a slot machine  1 . FIG. 2 presents a perspective view, as taken obliquely from the front, of a slot machine  1  according to this embodiment. 
     In FIG. 2, the slot machine  1  is provided at its casing  2  with a front panel  3  facing the player. At the back of this front panel  3 , there are rotatably mounted three reels  4 ,  5  and  6  which construct variable display means. On the outer circumference of each of the reels  4 ,  5  and  6 , there is illustrated a symbol column which is composed of a plurality of patterns (as will be called the “symbols”). Three of these symbols are observed through display windows  7 ,  8  and  9  which are opened in the front face of the front panel  3 . 
     Below the display windows  7 ,  8  and  9 , there are individually: a slot  10  for the player to insert three or less game coins for each game; a bet switch  12  for betting three or less game coins within a range of the credit balance without inserting the game coins into the slot  10 ; and a credit number display unit  13  composed of seven-segment LEDs or the like for displaying the credit balance. 
     In the display windows  7 ,  8  and  9 , there are illustrated three horizontal winning lines L 1 , L 2 A and L 2 B and two oblique winning lines L 3 A and L 3 B. On the lefthand side of the display window  7 , there are provided five effective line display lamps  11   a  to  11   e  corresponding to the individual winning lines L 1 , L 2 A, L 2 B, L 3 A and L 3 B. 
     When the player inserts one game coin into the slot  10  or depresses the bet switch  12  one time prior to the start of each game, the bet number is “1”. As shown in FIG. 3A, the center winning line L 1  is then exclusively effected, and the effective line display lamp  11   c  is lighted. When the player inserts two game coins into the slot  10  or depresses the bet switch  12  two times, the bet number is “2”. Then, all of the three horizontal winning lines L 1 , L 2 A and L 2 B are effected, as shown in FIG. 3B, and the effective line display lamps  11   b ,  11   c  and  11   d  are lighted. When the player inserts three game coins or depresses the bet switch  12  three times, the bet number is “3”. Then, all of the five horizontal and oblique winning lines L 1 , L 2 A, L 2 B, L 3 A and L 3 B are effected, as shown in FIG. 3C, and all the effective line display lamps  11   a  to  11   e  are lighted. 
     Below the bet switch  12 , there are disposed: a credit/payout switch (as will be shortly referred to as the C/P switch)  14  for switching the credit and payout of the game coins, as acquired by the player, in response to the depression of the player; a game start lever  15  for turning the reels  4 ,  5  and  6  altogether in response to the tiling operation of the player; and three stop button switches  16 ,  17  and  18  arranged to correspond to the respective reels  4 ,  5  and  6  for stopping the reels  4 ,  5  and  6 , respectively, in response to the depressions of the player. 
     In the upper portion of the front face of the casing  2 , there is disposed a prize display unit  19  for displaying combination tables enumerating the kinds of symbol combinations of prize modes and the numbers or the like of game coins to be paid back in response to the individual prize modes. In the lower portion of the front face of the casing  2 , there are disposed a coin payout tray  21  for reserving the game coins, as paid out through a coin payout chute  20 , and a speaker mouth  22  for outputting the various effect sounds, as emitted from a speaker in the casing  2 , to the outside. 
     Each of the symbol columns, as illustrated in the reels  4 ,  5  and  6 , is composed twenty one symbols, as shown in an exploded view of FIG.  4 . As the individual reels  4 ,  5  and  6  rotate in the direction of arrow X, those symbols reciprocally move in the same direction. 
     Here, each of the aforementioned symbol columns having twenty one symbols is composed of totally seven kinds of symbols: patterns of the numeral “7”, as called the “Seven”; patterns bearing letters “JAC” on plums, as called the “JAC”; patterns of a bell, as called the “Bell”; patterns bearing letters “MAGNUM”, as called the “magnum”; patterns of a bullet, as called the “Bullet”; and patterns of two kinds of white and black letters “BAR”, as called the “Bar”. 
     When the reels  4 ,  5  and  6  are stopped in response of the depressions of the stop button switches  16 ,  17  and  18  by the player, moreover, the prize of the mode, as lotted at random, is determined if the combination of the symbols arrayed on any of the effected winning lines L 1 , L 2 A, L 2 B, L 3 A and L 3 B coincides with the combination of the symbols of the prize mode. 
     FIG. 5 shows the content of the symbol combination table which is illustrated in the prize display unit  19 . In this combination table, the symbol combinations, as appearing in a lefthand upper column A, a lefthand lower column B and a righthand upper column C, illustrate the kinds of high bonus modes, as called the “bonus mode”, and the symbol combinations, as appearing in a righthand lower column D, illustrate the kinds of low bonus mode, as called “small mode”. 
     Specifically, when the three symbols on the aforementioned effect winning line are all the “Seven”, as illustrated in the lefthand upper column A, or when the two symbols are the “Bar” and the one symbol is the “Seven”, fifteen game coins are paid back, and the “BB” game is then performed. When the three symbols on the effective winning line are all the “Bar”, as illustrated in the lefthand lower column B of the same table, fifteen game coins are paid back, and the “RB” game is then performed. When the three symbols on the effective winning line are all the “Magnum”, on the other hand, as illustrated in the righthand upper column C of the same table, four game coins are paid back, and the “SB” game is then performed. When the three symbols on the effective winning line are all the “Bell”, as illustrated in the righthand lower column D of the same table, moreover, ten game coins are paid back; when the lefthand one of three symbols is the “Bullet”, two game coins are paid back; and when three symbols are all the “JAC”, another game (or replay) is offered. 
     The probabilities for these prize modes to occur are stored in advance as the data in the prize decision table which is referred to for the random sampling, as will be described hereinafter. As shown in FIG. 6A, more specifically, the prize decision table is constructed to have the individual data of Lottery Probability, No. of Lottery Random Numbers, Total of Random Numbers, Bonus Coin No. and Expected Value and so on for each prize mode. 
     Here, the “Total of Random Numbers” is the total RDM of the random numbers which are generated by a random sampling for lotting a prize mode. In this embodiment, RDM=16384 because the random numbers are generated within a range of 0 to 16383. 
     The “No. of Lottery Random Numbers” is the number of random numbers which are present in the range assigned to each prize mode by assigning a random number in the range of 0 to 16383 to a specific range for each prize mode. Specific numbers r   1   to r   6   are set for the individual prize modes. 
     The “Lottery Probability” is expressed by the ratios of the numbers of lottery random numbers r   1   to r   6   to the total RDM of random numbers for each prize mode and is represented by a   1   =r   1   /RDM for the “BB game”. 
     The “Bonus Coin No.” is expressed by the numbers M   1   to M   6   of coins to be paid back for the individual prize modes and is determined for each prize mode. 
     The “Expected Value” is determined for each prize mode on the basis of the following Formula (3). Here in Formula (3), the symbol combination number is the total of combinations, which can be made of the above-specified seven kinds of symbols, such as 9261 together with a reeling number: 
     
       
         R i =(No. of Lottery RN)/(Total of RN)×(Bonus Coin Numbers)×1/(Bet No.)×(Reeling No.)/(Symbol Combination No.)=r   1   /RDM×M   1   ×1/3×9261/9261  (3); 
       
     
     wherein RN: the random numbers. 
     Moreover, the total (or expected value total) R T  of expected values R i  (wherein letter i indicates the No. of each prize mode) of the individual prize modes is no more than the proper expected value (e.g., 0.9) which is determined advance for each game state, as expressed by the following Formula (4):                R   T     =         ∑     i   =   1     6                   Ri     ≤     Rmax   .               (   4   )                                
     Moreover, the prize decision table, as shown in FIG. 6A, is also provided for the ordinary probability game and the high probability game. 
     More specifically, the prize decision table to be used in the ordinary probability game is composed of the numerical data, as shown in FIG. 6B, and the total expected value R T  is set at 0.38733. On the other hand, the prize decision table to be used in the high probability game is constructed of the numerical data, as shown in FIG. 6C, and the total expected value R T  is set at 0.88867. 
     In FIG. 6C, the number of lottery random numbers for the “SB game” is  7120 , which is ten times as high as the number of  712  in the prize decision table shown in FIG.  6 B. For the “SB game”, therefore, the lottery probability and the expected value are ten times as high as those for the “SB game” in the prize decision table shown in FIG. 6B, so that the probability for the “SB game” to be lotted is raised to ten times by the random sampling, as will be described hereinafter. 
     If the number of lottery random numbers for the “SB game” were merely raised to ten times, the total expected value R T  would exceed the proper expected value Rmax. By lowering the number of the lottery random numbers for the “Bell” or the low bonus mode from 819 to 720, therefore, the total expected -value R T  of the prize decision table, as shown in FIG. 6C, is adjusted to 0.88867 no more than the proper expected value Rmax. 
     FIG. 7 shows a circuit construction including a control unit  23  for controlling the game processing operations in the slot machine  1 , and peripheral devices electrically connected with the control unit  23 . 
     As shown in FIG. 7, the control unit  23  is constructed to include: a microprocessor (MPU)  26  provided with a read only memory (ROM)  24  and a random access memory (RAM)  25 ; a clock circuit  27  for generating an operation clock signal of the MPU  26 ; and a random number setting unit  28  for setting a random number to be sampled. 
     The ROM  24  is stored with not only a game processing procedure to be executed in the slot machine  1  as a sequence program but also prize decision tables or the like for the ordinary probability game and the high probability game, as shown in FIGS. 6B and 6C. The RAM  25  is provided with a storage region for storing the various processing data or flag data when the MPU  26  processes according to the aforementioned sequence program. 
     The clock circuit  27  is constructed to include a clock pulse generating circuit  29  for generating a reference clock signal of a predetermined frequency, and a divider  30  for generating a clock signal for operating the MPU  26  by dividing the frequency of the reference clock signal. 
     The random number setting unit  28  is constructed to include a random number generator  31  for generating a random number within a predetermined range (e.g., 0 to 16383) in response to a command of the MPU  26 , and a random sampling circuit  32  for sampling an arbitrary random number RD from the random numbers generated by the random number generator  31 , and transferring the sampled random number RD to the MPU  26 . 
     With a plurality of input/output ports (or I/O ports) of the MPU  26 , there are connected: the bet switch  12 ; the C/P switch  14 ; the game start lever  15 ; the coin sensor  33  for detecting the game coin inserted into the slot  10 ; a motor drive circuit  34 ; areel position detect circuit  35 ; areel stop signal circuit  36 ; a hopper drive circuit  37 ; a pay completion signal generating circuit  38 ; a display drive circuit  39 ; a speaker drive circuit  40 ; and a lamp drive circuit  41 . 
     With the motor drive circuit  34 , there are connected stepping motors  42 ,  43  and  44  for driving the reels  4 ,  5  and  6  rotationally. The stop button switches  16 ,  17  and  18  are connected with the reel stop signal circuit  36 . When the player tilts the game start lever  15 , the MPU  26  detects this tilt to cause the motor drive circuit  34  to start feed drive pulses to the stepping motors  42 ,  43  and  44  thereby to rotate the reels  4 ,  5  and  6 . When the stop button switches  16 ,  17  and  18  are depressed, on the other hand, the reel stop signal circuit  36  detects the depressions and transfers its detect signal to the MPU  26 . In response to this detect signal, moreover, the MPU  26  causes the motor drive circuit  34  to stop the feed of the drive pulses to the stepping motors  42 ,  43  and  44  thereby to stop the reels  4 ,  5  and  6 . 
     The reel position detect circuit  35  is provided with an optical sensor or the like for detecting the rotational positions (or rotational angles) of the reels  4 ,  5  and  6 , so that the position detect signals detected by the optical sensor or the like are transferred to the MPU  26  to inform the positional data of the individual symbols illustrated on the reels  4 ,  5  and  6 . 
     With the hopper drive circuit  37 , there is connected a reservoir hopper  45  for reserving the game coins. With the pay completion signal generating circuit  38 , there is connected a coin detect unit  46  for counting the number of game coins to be paid back for a prize from the reservoir hopper  45  to the coin payout tray  21 . When the counted value of coins actually paid back reaches a predetermined bonus coin number data, a pay completion signal is transferred from the pay completion signal generating circuit  38  to the MPU  26 . 
     With the display drive circuit  39 , there are connected the effective line display lamps  11   a  to  11   e  and the credit number display  13 , so that the display drive circuit  39  causes the display lamps  11   a  to  11   e  and the displays  13  and  14  to make displays in accordance with the instructions of the MPU  26 . 
     With the speaker drive circuit  40 , there is connected a speaker  47  for outputting sound effects through the speaker mouth  22 . With the lamp drive circuit  41 , there is connected back lamps  48  for illuminating the symbols, as appearing through the display windows  7 ,  8  and  9 , from the back side. 
     Next, the operations of the present slot machine  1  to be controlled by the control unit  23  will be described with reference to the flow charts shown in FIGS. 8 to  15 . 
     In FIG. 8, the MPU  26  decides at first (or at step [as will be shortly referred to as the “ST”]  1 ) whether or not the coin BET has been made. This answer is “YES” when the coin was inserted into the slot  10  to make the detect signal input from the coin sensor  33  or when the signal input from the BET switch  12  was made. When “YES”, it is then decided (at ST 2 ) whether or not the game start lever  15  was operated. When this answer is “YES”, the MPU  26  commands the motor drive circuit  34  to drive all the reels  4 ,  5  and  6  rotationally (at ST 3 ). After this, a prize is decided (at ST 4 ). This decision is made according to the later-described procedures of the flow charts of FIGS. 10 to  12 . 
     The prize flags to be set in this prize decision are one to be set at subsequent steps (i.e., ST 34  and ST 35 ), when the answer (of ST 32 ) based on the random sampling of FIG. 10 is “YES”, and the other to be set at subsequent steps (i.e., ST 48 , ST 53  and ST 55 ) when the answer (of ST 47 ) based on the random sampling of FIG. 12 is “YES”. 
     In accordance with the kind of the prize flag set as a result of the aforementioned prize decision, the reel stop is controlled (at ST 5 ). It is then decided (at ST 6 ) what prize mode the symbol combination at the reel stop belongs to. When this answer is “NO”, the routine returns to ST 1 . When the answer is “YES”, it is further decided (at ST 7 ) whether or not the symbol combination at the reel stop time is the aforementioned “Replay” game. When this answer is “NO”, a predetermined number of coins are paid back (at ST 8 ), and the routine transfers to subsequent steps (of FIG.  9 ). When the answer is “YES”, no coin is paid back, and the routine returns to the decision (of ST 2 ) of the aforementioned operation of the start lever  15 . 
     Next, as shown in FIG. 9, it is decided (at ST 10 ) whether or not the prize pattern at the aforementioned reel stop time is the “BB game”. When this answer is “YES”, the routine advances to the flow chart of the “BB game” shown in FIG.  13 . When the answer is “NO”, it is then decided (at ST 11 ) whether or not the prize pattern is the “RB game”. When this answer is “YES”, the routine advances to the flow chart of the “RB game” shown in FIG.  14 . When not the “BB game” nor “RB game”, it is decided (at ST 12 ) whether or not the prize pattern is the “SB game”. When this answer is “YES”, the routine advances to the flow chart of the “SB game” shown in FIG.  15 . When the answer is “NO”, the routine returns to the first step (i.e., ST 1 ) of all the operations shown in FIG.  8 . 
     Next, the operation of the prize decision of step  4  of FIG. 8 will be described with reference to the flow charts of FIGS. 10 to  12 . The random sampling to be used for this prize decision is performed by using the random number generator  31  and the random sampling circuit  32 . 
     In FIG. 10, it is decided at first (at ST 20 ) whether the present game is the “SB game” or a bonus game in the “RB game” or “BB game”. 
     In the case of the bonus game, the random sampling is performed (at ST 21 ), and it is decided (at ST 22 ) whether or not the random number value is no more than a predetermined value R   1   . Here, when the random number to be sampled is within a range of 0 to 16383 and if R   1   =14744, the probability of random number≦R   1   is 14744/16384≈9/10, and the probability of random number &gt;Ris (16384−14744)/16384≈1/10. 
     Next, when the aforementioned decision answer of the random number is “NO”, the RAM  25  is set (at ST 23 ) with the flag of a “Blank” game. When the answer is “YES”, the RAM  25  is set (at ST 24 ) with the flag of the “JAC” game (in which “JAC”-“JAC”-“JAC” are aligned on the center winning line L 1 ), and the routine of the present flow is ended. 
     When the answer of the first ST 20  is “NO” (that is, when not the bonus game), on the contrary, it is decided (at ST 25 ) whether or not the present game is in the “BB game”. When this answer is “YES”, the routine transfers to the first step (i.e., ST 36 ) of FIG.  11 . When the answer is “NO”, it is decided (at ST 26 ) whether or not the BB flag has already been set. When this answer is “YES”, the routine transfers to the first step (i.e., ST 36 ) of FIG.  11 . When the BB flag is not set, it is decided (at ST 27 ) whether or not the game is in the RB. When this answer is “YES”, the routine transfers to the first step (i.e., ST 36 ) of FIG.  11 . 
     When the BB flag and the RB flag are not set, it is then decided (at ST 28 ) whether or not the existing game is in the “SB high probability game state” (or whether or not the SB high probability game state has been set before the present game). When in the “SB high probability game state”, moreover, the prize decision table for extinguishing the “SB high probability game state” is set (at ST 29 ). When not in the “SB high probability game state” (that is, when in the “SB ordinary probability game state”), the prize decision table for establishing the “SB high probability game state” is set (at ST 30 ). 
     Here, the table for extinguishing the “SB high probability game state” has only one digit (e.g.,  105 ) as the data to be compared with the random value sampled at next step  31 , but the table for establishing the “SB high probability game state” is provided with a predetermined number (e.g., six) of data within a predetermined range (10 to 20). This is because a plurality of stages may be interchanged by operating the switches disposed in the control board box or in the system, for example, so that the payout ratio of the slot machine may be arbitrarily set on the side of the game house. Therefore, the data of the table, as compared with the random value sampled at the following step  31 , for establishing the “SB high probability game state” are determined to one of the six data, for example, at the stage when the power source of the machine is turned ON. 
     Next at step  31 , the random sampling is executed within a predetermined range (e.g., a range of 0 to 16383), and it is decided (at ST 32 ) whether or not this sampled random value is no more than the predetermined value R   2   (e.g., 105 in the case of the table for the extinguishment, and one of 11 to 21 determined in advance by the switch operations in the case of the table for the establishment). The probability for the decision answer “YES” is 105/16384≈1/156, when the set table is for the extinguishment, and (11/16384)˜(21/16384)≈(1/1489)˜(1/780), when the set table is for the establishment. 
     When the answer of the step  32  is “NO”, the routine transfers to the first step of FIG.  11 . When the answer is “YES”, it is decided (at ST 33 ) whether or not the set table is for the extinguishment. When this answer is “YES”, the flag of the “SB ordinary probability game” is set (at ST 34 ). When the set table is for the establishment, on the other hand, the flag of the “SB high probability game” is set (at ST 35 ). 
     Next, the routine advances to the operations of FIG.  11 . First of all, the prize decision table for “in the BB game” is set for the reference (at ST 36 ), and it is decided (at ST 37 ) whether or not the present game is in the BB game. When this answer is “YES”, the routine transfers to the later-described step (i.e., ST 45 ), at which the leading address of the data to be referred to at the prize decision table is set. 
     When the answer of ST 37  is “NO”, the prize decision table for “in the RB game” is set (at ST 40 ). Next, it is decided (at ST 41 ) whether or not the present game is in the RB game. When this answer is “YES”, the routine transfers to the later-described ST 45 , at which the leading address of the data to be referred to in the prize decision table is set. When the present game is not in the RB game, on the contrary, the prize decision table for “in the SB high probability game”, as shown in FIG. 6C, is set (at ST 42 ). 
     It is then decided (at ST 43 ) whether or not the present game is “in the SB high probability game”. When this answer is “YES”, the routine transfers to ST 45 , at which the leading address of the data to be referred to in the prize decision table is set. When not in the SB high probability game, on the contrary, the prize decision table for “in the SB high probability game” is reset, and the prize decision table for the “SB ordinary probability game” is set (at ST 44 ). 
     The prize decision tables for the aforementioned “in the BB game”, “in the RB game”, “in the SB high probability game” and the “SB ordinary probability game” are individually provided with six data, as schematically shown in FIG.  16 . 
     Each data is provided with the flags of prize modes and different numerical values as the data to be compared with the random value at the following step (i.e., at ST 47 ). In FIG. 16, for example, the flags of prize modes (A), (B) and (C) are for the “BB game”, “RB game” and “SB game”, respectively, and the flag of prize mode (D) is for the “Replay” game. 
     At a next step (i.e., ST 46 ), the random sampling is performed within the range of 0 to 16383, and it is decided (at ST 47 ) whether or not the sampled random value is no more than R   3   , as shown in FIG.  12 . At this time, the sampled random value is compared with the leading data “(A)” of the prize decision table as the value R   3   . 
     When the data (A) has a numerical value of  44  and when the sampled random value is  37 , for example, this is smaller than R   3   so that the answer of ST 47  is “YES”. At the next step (i.e., ST 48 ), the flag (i.e., “BB game”) of the data is set (at ST 48 ). Hence, the probability of setting this flag is 44/16384≈1/372. 
     When the answer of ST 47  is “NO”, the data (B) of the next address is set to R 3 . So long as the data end is not decided at the next step (i.e., ST 50 ), the routine returns to ST 47 , at which the sampled random value and the value R 3  are compared. This operation is performed till the data end (e.g., six times in the table example of FIG.  16 ). When the answer of ST 50  is “YES”, the corresponding prize mode is absent so that the “Blank” flag is set at ST 48 . 
     Next, it is decided (at ST 51 ) whether or not the “BB game” flag or the “RB game” flag is set. When this answer is “NO”, the routine is ended. When the answer is “YES”, it is then decided (at ST 52 ) whether or not the “SB high probability game state” has prevailed before the start of the present game, that is, whether or not the “SB high probability game state” flag has been set before the game start. When this answer is also “YES”, moreover, the routine is ended by resetting the “SB high probability game state” flag and by setting the “SB ordinary probability game”. 
     When the answer of ST 52  is “NO”, on the contrary, it is decided (at ST 54 ) whether or not the flag for generating the “SB high probability game state” has been set. When this answer is “YES”, that is, when the prize decision of the present game has revealed that both the “BB game” flag or the “RB game” flag and the “SB high probability game state” flag are set, the routine is ended by resetting the “SB high probability game state” flag and by setting the “SB ordinary probability game state” flag (at ST 55 ). 
     In case it is thus found by the prize decision that the “BB game” flag or the “RB game” flag is set, the “SB high probability game state” flag is reset not only when the “SB high probability game state” flag is set at the present prize decision but also when the “SB high probability game state” flag was set at and before the present game. 
     Here will be described the operation procedure of the “BB game” with reference to FIG.  13 . 
     First of all, it is decided (at ST 60 ) whether or not the game number is over 30 times. When this answer is “YES”, the routine returns to the first step (ST 1 ) of all the operations, as shown in FIG.  8 . When the game number is below 30 times, it is decided (at ST 61 ) whether or not the coin BET has been made. 
     This answer is “YES” as at ST 1  of FIG. 8, when the coin was inserted into the slot  10  so that the input from the coin sensor  33  is made or when the input from the BET switch  12  is made. In this case, it is then decided (at ST 62 ) whether or not the game start lever  15  has been operated. When this answer is “YES”, the MPU  26  feeds the motor drive circuit  34  with the drive signal to drive all the reels  4 ,  5  and  6  rotationally (at ST 63 ). 
     After this, the prize is decided (at ST 64 ). This decision corresponds to that of ST 47  of FIG. 12 after the prize decision table for “in the BB game” was set at ST 36  of FIG. 11, as described hereinbefore. 
     As a result of this prize decision, the stop of the reels  4  to  6  is controlled (at ST 65 ) according to the kind of the set prize flag. It is then decided (at ST 66 ) whether or not the display at the reel stop time is a predetermined prize pattern. When this answer is “NO”, the routine returns to ST 60 . When the answer is “YES”, a predetermined number of coins are paid back (at ST 67 ), and the routine transfers to ST 68 . 
     At ST 68 , it is decided whether or not the game is the bonus game. When this answer is “NO”, the routine returns to ST 60 . When the answer is “YES”, it is decided (at ST 69 ) whether or not the bonus game has been played twelve times. When this answer is “YES”, the routine transfers to the later-described ST 77 , at which it is decided whether or not the bonus game is a second set. When this answer is “YES” (that is, when the bonus game is played at the second set), the routine returns to the first step (i.e., ST 1 ) of all the operations shown in FIG.  8 . When the answer is “NO”, the routine returns to ST 60 . 
     When it is decided at ST 69  that the bonus game is not played twelve times, on the contrary, it is decided (at ST 70 ) like before whether or not the coin BET has been made. When this answer is “NO”, the routine returns to ST 69 . When the answer is “YES”, all the reels  4 ,  5  and  6  are rotationally driven (at ST 71 ). After this, the prize is decided (at ST 72 ). This decision corresponds to that of ST 22  of FIG.  10 . 
     As a result of this prize decision, the stop of the reels  4 ,  5  and  6  is controlled (at ST 73 ) according to the kind of the set prize flag. It is then decided (at ST 74 ) whether or not the symbol combination at the stop time of the reels  4  to  6  corresponds to any of the prize modes. When the answer is “NO”, the routine returns to ST 69 . 
     Next, a predetermined number of coins are paid back (at ST 75 ), and it is then decided (at ST 76 ) whether or not the prize is the eighth. When this answer is “NO”, the routine returns to ST 69 . When the answer is “YES”, it is decided (at ST 77 ) whether or not the bonus game is at the second set. When this answer is “NO”, the routine returns to ST 60 . When the answer is “YES”, the routine returns to the fist step (i.e., ST 1 ) of all the operations shown in FIG.  8 . 
     Here will be described the operation procedures of the “RB game” with reference to FIG.  14 . 
     It is decided (at ST 80 ) whether or not the bonus game in the “RB game” has been played twelve times. When this answer is “YES”, the routine returns to the first step (i.e., ST 1 ) of all the operations shown in FIG.  8 . When the answer is “NO”, it is decided (at ST 81 ) whether or not the coin BET has been made. When this answer is “NO”, the routine returns to ST 80 . When the answer is “YES”, all the reels  4 ,  5  and  6  are rotationally driven (at ST 82 ). After this, the prize is decided (at ST 83 ). This corresponds to the decision of ST 22  of FIG.  10 . 
     As a result of this prize decision, the stop of the reels  4  to  6  is controlled (at ST 84 ) according to the kind of the set prize flag. It is then decided (at ST 85 ) whether or not the display at the stop time of the reels  4  to  6  is a predetermined prize pattern. When this answer is “NO”, the routine returns to ST 80 . When the answer is “YES”, a predetermined number of coins are paid back (at ST 86 ). After this, it is decided (at ST 87 ) whether or not the prize number is the eighth. When this answer is “NO”, the routine returns to ST 80 . When the answer is “YES”, the routine returns to the first step (i.e., ST 1 ) of all the operations shown in FIG.  8 . 
     Here will be described the operation procedure of the “SB game” with reference to FIG.  15 . 
     First of all, it is decided (at ST 90 ) like before whether or not the coin BET has been made. When this answer is “NO”, a standby is made as it is. When the answer is “YES”, it is decided (at ST 91 ) whether or not the game start has been instructed by the operation of the game start lever  15 . When this answer is “YES”, all the reels  4 ,  5  and  6  are rotationally driven (at ST 92 ). After this, the prize is decided (at ST 93 ). This corresponds to the decision of ST 22  of FIG.  10 . 
     As a result of this prize decision, the stop of the reels  4  to  6  is controlled (at ST 94 ) according to the kind of the set prize flag. It is then decided (at ST 95 ) whether or not the display at the stop time of the reels  4  to  6  is a predetermined prize pattern. When this answer is “NO”, the routine returns to the first step (i.e., ST 1 ) of all the operations shown in FIG.  8 . When the answer is “YES”, a predetermined number of coins are then paid back (at ST 96 ), and the routine returns to the first step (i.e., ST 1 ) of all the operations shown in FIG.  8 . 
     As has been described hereinbefore, according to the slot machine  1  of this embodiment, by adjusting not only the number of lottery random numbers of a specific mode (e.g., the SB game) in the prize decision table to be applied in the ordinary probability game state and in the prize decision table to be applied in the high probability game state but also the number of lottery random numbers for another mode (e.g., the Bell), the total R T  of the expected values in the individual prize decision tables is set to the proper expected value Rmax or less. This can avoid in advance the problem that the so-called “payout ratio” becomes excessively high. As a result, a proper game mode can be provided for the player and a game machine which will impose no economical burden can be realized for the game house. 
     Here, this embodiment has been described on the case in which the total R T  of the expected values of the prize decision table to be applied in the high probability game state is adjusted to the proper expected value Rmax or less by adjusting only the number of lottery random numbers for another mode “Bell”. By adjusting the number of lottery random numbers for one another mode such as the “Replay” or “Bullet” or the number of lottery random numbers for a plurality of modes, however, the total R T  of the expected values of the prize decision table may be adjusted to the proper expected value Rmax or less. 
     Although the present invention has been explained in reference to the embodiments, it is apparent for those skilled in the art that many changes and modifications can be made without departing from the spirit and scope of the invention, as clear from the following claims.