Abstract:
A cooking oven, wherein air in a cooking chamber is sucked into a blower on the outside of the cooking chamber and fed to an upper duct and a lateral duct, air current led into the upper duct is heated by an upper heater and re-circulated from an upper blowing port to the cooking chamber, a catalyst block heated by a catalyst heating heater is disposed in the upper duct to decompose lamp black and smell substances contained in the air current, catalyst paint is applied onto the inner wall surface of the upper duct to reinforce a performance for decomposing the lamp black and smell substances, both the lateral duct and the upper duct are formed in the same structure, the distributions of heating volumes of the upper heater and the lateral heater in the cross sections of the upper duct and the lateral duct are set so that larger heating volumes are generated on larger air volume sides according to the air volume distributions in the cross sections of the ducts, and the catalyst block is also disposed in the cross sections of the ducts eccentrically to the larger heater heating volume side.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to a cooking oven that cooks foods with heat by application of a hot air stream thereto. 
   DESCRIPTION OF RELATED ART 
   Cooking ovens such as convention ovens and hot-air-impingement ovens that cook foods with heat by forming a circulated current of hot air stream inside a cooking chamber in which foods are placed, are well known and widely used. Published documents such as, to name a few, Japanese Utility Model Published No. H6-23841 and Japanese Patent Applications Laid-Open Nos. H9-145063, Hi1-166737, 2000-329351, and 2001-311518 disclose examples of hot-air-circulation cooking ovens. On the other hand, Japanese Patent Published No. H9-503334 discloses an example of a hot-air-impingement cooking oven. Among these examples, the cooking oven disclosed in Japanese Patent Application Laid-Open No. 2001-311518 has a heater arranged inside a duct through which a air stream is sent to a cooking chamber. 
   Now, as the basis of the present invention, the construction of a hot-air-circulation cooking oven will be described with reference to  FIGS. 33 and 34 .  FIG. 33  is a front view of the cooking oven, and  FIG. 34  is a vertical sectional view thereof. 
   The cooking oven  1  has a cabinet in the shape of a rectangular parallelepiped. Inside the cabinet  10 , there is formed a cooking chamber  11  in the shape of a rectangular parallelepiped. The top and bottom of the cooking chamber  11  are formed by a ceiling wall  12  and a floor wall  13 , respectively. Of the four sides of the cooking chamber  11 , three are formed by a rear inner wall  14 , a left inner wall  15 , and a right inner wall  16 , respectively, and the fourth side is formed by a freely openable door  17 . The door  17  and all the walls of the cooking chamber  11  are heat-insulated. 
   The cooking chamber  11 , which is enclosed from six sides by the walls and the door as described above, has the following interior dimensions: 230 mm high, 408 mm wide, and 345 mm deep. It should be understood that all the values given as dimensions, speeds, temperatures, and the like in the present specification are merely preferable examples and are not meant to limit the scope of the present invention in any way. 
   Outside the rear inner wall  14 , there is installed a blower  20 . The blower  20  has a centrifugal fan  22  arranged inside a fan casing  21 . This centrifugal fan  22  is rotated in the forward and backward directions by a reversible-rotation motor, which will be described later. The fan casing  21  is of a type that branches into two directions, and has an upper discharge port  23  and a side discharge port  24 . The upper discharge port  23  connects to an upper duct  25  provided outside the ceiling wall  12 . The side discharge port  24  connects to a side duct  26  provided outside the left inner wall  15 . 
   The upper duct  25  has an upper blowout port  30  open to the cooking chamber  11 . The side duct  26  has a side blowout port  31  open to the cooking chamber  11 . In the rear inner wall  14 , there is formed a suction port  32  of the blower  20 . The upper blowout port  30  is formed by a group of small cylindrical holes each 11 mm across. The side blowout port  31  and the suction port  32  are each formed by a group of small holes each 5 mm across. 
   As shown in  FIG. 34 , in the upper duct  25  is provided an upper heater  40 . In the side duct  26  is provided a side heater  41 . Outside the right inner wall  16 , there are arranged a microwave heating device  42  that assists the heating by the upper and side heaters  40  and  41  and a controller  43  that controls the operation of the cooking oven  1  as a whole. On the outer front surface of the right inner wall  16 , there is provided an operation panel  44  (see  FIG. 33 ) that accepts instructions for the controller  43 . 
   On the floor wall  13 , there is arranged a turntable  50  on which to place foods. On the turntable  50  is placed a supporting means such as a grill or rack that suits the kind of food placed. Reference number  51  represents a turntable drive motor. 
   The cooking oven  1  operates as follows. First, the door  17  is opened. Then, among different types of supporting means such as grills and racks, one that suits the intended kind of food is placed on the turntable  50 . On this supporting means, foods are placed directly or using a container. Then, the door  17  is closed. 
   After the door  17  is closed, cooking conditions are entered via the operation panel  44 . Based on the thus entered cooking conditions, the controller  43  selects the optimum among a plurality of pre-programmed cooking methods. The controller  43  then drives the blower  20 , upper heater  40 , side heater  41 , microwave heating device  42 , and turntable drive motor  51  to start cooking. 
   For example, in a case where roasted chicken is prepared, a grill is placed on the turntable  50 , and a chunk of meat is placed on the grill. Then, the door  17  is closed, and then, from the menu displayed on the operation panel  44 , “roasted chicken” is selected. Now, the controller  43  operates the blower  20 , upper heater  40 , side heater  41 , microwave heating device  42 , and turntable drive motor  51  in a mode for preparing “roasted chicken.” 
   The upper heater  40  has a power rating of 1,700 W, and the side heater  41  has a power rating of 1,200 W. Out from each of the upper blowout port  30  and the side blowout port  31  blows a hot air stream having a temperature of 300° C. or more as measured at those ports. The controller  43  controls the blower  20  in such a way that the air stream blown out from the upper blowout port  30  has a air stream speed of 65 km/h or more, and that the air stream blown out from the side blowout port  31  has a air stream speed of 30 km/h or less. The turntable  50  is rotated at a rotation rate of 6 rpm. 
   In the case described above, heating cooking is achieved by a hot-air-impact method whereby a high-speed hot air stream is blown onto foods. This permits fast cooking of the chunk of meat. The temperature inside the cooking chamber  11  is automatically adjusted at the target temperature entered via the operation panel  44 . The upper limit of the target temperature is 300° C. 
   Next, how sponge cake is prepared will be described. A rack is placed on the turntable  50 . Then, dough to be cooked into sponge cake is placed on the turntable  50  and also on the rack. The door  17  is closed, and, from the menu displayed on the operation panel  44 , “sponge cake” is selected. Now, the controller  43  operates the blower  20 , upper heater  40 , side heater  41 , microwave heating device  42 , and turntable drive motor  52  in a mode for preparing “sponge cake.” Also here, the turntable  50  is rotated at a rotation rate of 6 rpm. 
   Here, however, the controller  43  controls the blower  20  in such a way that a hot air stream having a air stream speed of 30 km/h or less blows out from the upper blowout port  30 , and that a hot air stream having a air stream speed of 40 km/h or less blows out from the side blowout port  31 . In this case, heating cooking is achieved by two-stage hot-air-circulation method, and this permits the dough placed on the turntable  50  and on the rack to be each cooked into fluffy sponge cake. The hot air stream that blows from above has a low speed, and thus does not deform by its pressure the dough in the process of rising. 
   In heating cooking, a hot air stream or a microwave may be used singly, or they may be generated simultaneously so that heating is achieved by their combined effect. Whether to use the effect of a hot air stream or a microwave alone or their combined effect is determined by a cooking program or through selection by the user. 
   The cooking oven  1  described above can cope with various kinds of food and various methods of cooking by adjusting the ratio of the volumes of air stream blown out by the blower  20 , the volumes of air stream themselves, and the air stream speeds, and by adjusting the amounts of heat generated by the upper and side heaters  40  and  41  and the output of the microwave heating device  42 . 
   As cooking is performed on the cooking oven  1  described above, foods release oil, fat, and odor substances. Such oil and fat, in the form of greasy fumes, soil the interior of the cooking chamber and ducts. They also settle on foods and spoil the flavor thereof. Odor substances, when exposed to heat, deteriorate. Such deteriorated odor substances, when they settle on foods, spoil the flavor thereof. 
   To overcome these inconveniences, proposals have conventionally been made to decompose greasy fumes and odor substances with a catalyst. For example, Japanese Patent Application Laid-Open No. H4-62324 discloses a construction wherein a deodorizing catalyst and a catalyst heating means are arranged inside a container in which food is heated. Japanese Patent Application Published No. 2000-510568 discloses a recirculation-type cooking oven provided with a catalyst converter. Japanese Patent Application Laid-Open No. HI0-202112 discloses a cooking oven wherein a catalyst coating is applied on interior paint. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a cooking oven that permits a catalyst to function satisfactorily and that can decompose greasy fumes and odor substances with high efficiency. 
   To achieve the above object, according to the present invention, a cooking oven is constructed as follows. The cooking oven has a blowout port and a suction port for passage of a hot air stream provided inside a cooking chamber and has a blower and a heat source for producing the hot air stream provided outside the cooking chamber so as to produce a circulated hot air stream inside the cooking chamber so that foods are cooked with heat by the circulated air stream. In this cooking oven, a catalyst block for decomposing substances released from foods and a heat source for heating the catalyst block are arranged inside the duct through which the hot air stream is fed to the blowout port. The heat source is so arranged as to face a plurality of faces of the catalyst block. With this construction, the catalyst block receives radiant heat from a plurality of directions, and thus quickly reaches the temperature that permits the catalyst to function. This permits the catalyst to start to function at an early stage. Moreover, of the plurality of faces of the catalyst block, one is made to face in the direction from which the circulated air stream blows. Thus, the circulated air stream heated by the heat source flows through the catalyst block. The catalyst block is heated from both inside and outside, and thus quickly reaches the temperature that permits the catalyst to function. In addition, of the plurality of faces of the catalyst block, another, i.e., one other than that facing in the direction from which the circulated air stream blows, is a face opposite thereto. Thus, not only the face that the circulated air stream blows directly onto but also the face opposite thereto is heated. This permits the catalyst to function satisfactorily irrespective of whether it is located on the upstream or downstream side of the air stream. 
   According to the present invention, a cooking oven is constructed as follows. The catalyst block is held by a fitting member in such a way as not to make contact with an interior wall surface of the duct. With this construction, the catalyst block does not make contact with an interior wall surface of the duct, and thus the heat of the catalyst block does not conduct to the walls of the duct. 
   According to the present invention, a cooking oven is constructed as follows. The cooking oven has a blowout port and a suction port for passage of a hot air stream provided inside a cooking chamber and has a blower and a heat source for producing the hot air stream provided outside the cooking chamber so as to produce a circulated hot air stream inside the cooking chamber so that foods are cooked with heat by the circulated air stream. In this cooking oven, catalyst paint for decomposing substances released from foods is applied to at least part of an interior wall surface of the duct through which the hot air stream is fed to the blowout port. With this construction, while the hot air stream is passing through the duct, substances released from foods are decomposed by the catalyst paint. Thus, even in a case where there is only a limited area for the arrangement of the catalyst, it is possible to exploit an interior wall surface of the duct to secure a sufficient contact-area between the catalyst and air stream. 
   According to the present invention, a cooking oven is constructed as follows. The cooking oven has a blowout port and a suction port for passage of a hot air stream provided inside a cooking chamber and has a blower and a heat source for producing the hot air stream provided outside the cooking chamber so as to produce a circulated hot air stream inside the cooking chamber so that foods are cooked with heat by the circulated air stream. In this cooking oven, a catalyst block for decomposing substances released from foods and a heat source for heating the catalyst block are arranged inside the duct through which the hot air stream is fed to the blowout port. The catalyst block is fitted at a distance from an interior wall surface of the duct. Moreover, catalyst paint for decomposing substances released from foods is applied to at least part of an interior wall surface of the duct. With this construction, the catalyst paint complements the function of the catalyst block, resulting in high-level decomposition. 
   Arranging the catalyst block in such a way as to completely obstruct the duct results in a high airflow resistance through the duct. This leads to a reduced amount of hot air stream or, if the desired amount of air stream is to be maintained, necessitates a blower with higher performance. This can be avoided by securing a gap between the catalyst block and an interior wall surface of the duct. Even when a gap is secured between the catalyst block and an interior wall surface of the duct to permit an air stream to pass therethrough in this way, unwanted substances contained in that air stream are decomposed by the catalyst paint. This helps obtain high-level decomposition performance. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. The surface to which the catalyst paint is applied has surface irregularities. With this construction, it is possible to increase the contact area between the catalyst paint surface and the air stream and thereby obtain still higher decomposition performance. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. Wave-shaped surface irregularities are formed on the interior wall surface of the duct. Of the slanted surfaces forming the surface irregularities, those facing in the direction from which the air stream blows are long and those facing in the direction opposite thereto are short. With this construction, it is possible to achieve efficient contact between the air stream and the catalyst paint surface and thereby obtain even higher decomposition performance. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. The surface irregularities are formed as ridges or grooves aligned along the air stream. With this construction, it is possible to increase the contact area between the catalyst paint surface and the air stream without diminishing the flow speed of the air stream. This makes it possible to obtain high-level decomposition performance even when the amount of hot air stream is large. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. The catalyst paint is applied to a air-stream-regulating plate provided inside the duct for regulating the air stream flowing toward the blowout port. With this construction, the air stream surely makes contact with the catalyst paint, permitting the catalyst to function satisfactorily. 
   According to the present invention, a cooking oven is constructed as follows. The cooking oven has a blowout port and a suction port for passage of a hot air stream provided in a wall of a cooking chamber and has a blower and a duct provided outside the cooking chamber, the blower sucking in air through the suction port and the duct directing the air blown out from the blower to the blowout port and heating the air with a heater incorporated therein, so as to produce a circulated hot air stream inside the cooking chamber so that foods are cooked with heat by the circulated air stream. In this cooking oven, a catalyst block for decomposing substances released from the foods is arranged inside the duct, and the distribution of the amount of heat generated by the heater within a cross section of the duct is so set as to be commensurate with the distribution of the amount of air stream within that cross section so that an increasingly large amount of heat is generated as there is an increasingly large amount of air stream. With this construction, the catalyst block is quickly heated by the hot air stream that flows through the duct, and thus the catalyst starts to function satisfactorily at an early stage. Moreover, the air flowing through that part of the cross section of the duct where the amount of air stream is large is given a commensurately large amount of heat. This helps achieve appropriate distribution of the amount of air stream and the amount of heat generated, resulting in efficient heating of air. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. The duct has a bent portion at a midpoint thereof. The heater is arranged at or on the downstream side of the bent portion, and the distribution of the amount of heat generated by the heater is so set that an increasingly large amount of heat is generated from the inner side to the outer side of the bent portion. With this construction, the large amount of air stream that flows at the outer side of the bent portion of the duct is given a commensurately large amount of heat. This helps achieve, in the duct having the bent portion, appropriate distribution of the amount of air stream and the amount of heat generated, resulting in efficient heating of air. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. The catalyst block is so arranged as to lie lopsided toward the side of a cross section of the duct where the amount of heat generated by the heater is larger. With this construction, the catalyst block is heated quickly, and is kept at a high temperature. This permits the catalyst to function fully. 
   According to the present invention, the cooking oven constructed as described above is constructed as follows. The catalyst block is fitted to an interior wall of the duct at the side thereof where the amount of heat generated by the heater is larger. With this construction, through heat conduction by way of the walls of the duct in addition to through direct heat radiation, the catalyst block is heated efficiently. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic vertical sectional view showing a first embodiment of a cooking oven according to the invention. 
       FIG. 2  is a schematic horizontal sectional view of the cooking oven of the first embodiment. 
       FIG. 3  is a perspective view of the catalyst block and the catalyst heater. 
       FIG. 4  is a sectional view showing how a hot air stream passes through the catalyst block. 
       FIG. 5  is a front view of a principal portion, showing how the catalyst block is fitted. 
       FIG. 6  is a perspective view of the catalyst block fitting member. 
       FIG. 7  is a front view of a principal portion, like  FIG. 5 , of a second embodiment of a cooking oven according to the invention. 
       FIG. 8  is a perspective view of the catalyst block portion, showing a third embodiment of a cooking oven according to the invention. 
       FIG. 9  is a perspective view of the fitting member of the third embodiment. 
       FIG. 10  is a perspective view of the fitting member, showing a fourth embodiment of a cooking oven according to the invention. 
       FIG. 11  is a perspective view of the fitting member, showing a fifth embodiment of a cooking oven according to the invention. 
       FIG. 12  is a front view of a principal portion, like  FIG. 5 , of a sixth embodiment of a cooking oven according to the invention. 
       FIG. 13  is a perspective view of the fitting member of the sixth embodiment. 
       FIG. 14  is a perspective view of the fitting member, showing a seventh embodiment of a cooking oven according to the invention. 
       FIG. 15  is a front view of a principal portion, like  FIG. 5 , of an eighth embodiment of a cooking oven according to the invention. 
       FIG. 16  is an enlarged partial sectional view showing a ninth embodiment of a cooking oven according to the invention. 
       FIG. 17  is an enlarged partial sectional view showing a tenth embodiment of a cooking oven according to the invention. 
       FIG. 18  is an enlarged partial sectional view showing an eleventh embodiment of a cooking oven according to the invention. 
       FIG. 19  is a partial vertical sectional view showing a twelfth embodiment of a cooking oven according to the invention. 
       FIG. 20  is a partial vertical sectional view showing a thirteenth embodiment of a cooking oven according to the invention. 
       FIG. 21  is an enlarged view of the portion shown in ellipse A in  FIG. 21 . 
       FIG. 22  is a schematic horizontal sectional view showing a fourteenth embodiment of a cooking oven according to the invention. 
       FIG. 23  is a partial sectional view taken along line B-B shown in  FIG. 22 . 
       FIG. 24  is a partial sectional view, like  FIG. 23 , showing a fifteenth embodiment of a cooking oven according to the invention. 
       FIG. 25  is a schematic vertical sectional view showing a sixteenth embodiment of a cooking oven according to the invention. 
       FIG. 26  is a schematic vertical sectional view showing a seventeenth embodiment of a cooking oven according to the invention. 
       FIG. 27  is a schematic horizontal sectional view of the cooking oven of the seventeenth embodiment. 
       FIG. 28  is a partial perspective view showing the arrangement of the horizontal heater and the catalyst block relative to each other. 
       FIG. 29  is a front view showing an eighteenth embodiment of a cooking oven according to the invention, showing it in perspective. 
       FIG. 30  is a vertical sectional view of the cooking oven of the eighteenth embodiment. 
       FIG. 31  is a perspective view of a principal portion of a nineteenth embodiment of a cooking oven according to the invention. 
       FIG. 32  is a perspective view of a principal portion of a twelfth embodiment of a cooking oven according to the invention. 
       FIG. 33  is a front view of a conventional cooking oven, showing it in perspective. 
       FIG. 34  is a vertical sectional view of the above conventional cooking oven. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, a first embodiment of a cooking oven according to the invention will be described with reference to  FIGS. 1 to 6 . The cooking oven  1  of the first embodiment is constructed in a similar manner to the cooking oven  1  shown in  FIGS. 33 and 34 , and therefore, here, only such components as are relevant to the invention are illustrated. Of the components of the cooking oven  1 , those which are common to the cooking oven  1  are identified with the same reference numbers as used earlier for them, and their explanations will not be repeated. The same principle is applied also to the second and following embodiments; that is, such components as have already been described are identified with the same reference numbers as used earlier for them, and their explanations will not be repeated unless necessary. 
   As shown in  FIGS. 1 and 2 , inside the upper duct  25  of the cooking oven  1 , there is provided a catalyst block  70 . The catalyst block  70  is arranged in an upstream-side portion inside the upper duct  25 . The catalyst block  70  is shaped as shown in  FIG. 3 . Specifically, the catalyst block  70  is provided with a carrier block  71  in the shape of a rectangular parallelepiped having a large number of tubular vent ports  72  stacked up in the shape of a honeycomb, and this carrier block  71  supports a catalyst. As the carrier block  71  is used a “CORDURITE” honeycomb or a stainless steel corrugate honeycomb. A steel plate having an alloy of aluminum and zinc plated thereon, i.e., a GALVALUME steel plate, or a Galvalume steel plate subjected to chromate treatment may be used as the base material for the carrier member. 
   As the catalyst is used one based on a precious metal such as platinum or palladium or one based on manganese such as MnO, MnO 2 , or Mn perovskite. To make the carrier block  71  support the catalyst, the former is painted, impregnated, or treated in any other manner with the latter depending on the material of the carrier block  71 . 
   The catalyst block  70  needs to be used in a temperature range that permits it to function satisfactorily. To achieve this, as a heat source for heating the catalyst block  70 , there is provided a catalyst heater. The upper heater  40 , which is the main heat source for producing the hot air stream, is shared as the catalyst heater. In the first embodiment, the upper heater  40  is realized with a sheath heater, and part of it is laid near the catalyst block  70  so as to serve as the catalyst heater  73 . 
   The catalyst block  70  is arranged in such a way that the air stream passes through the inside of the tubular vent ports  72 , i.e., in such a way that the length direction of the block as a whole is perpendicular to the air stream. This arrangement is shown in  FIG. 4 . The catalyst heater  73  is so formed as to face both the upstream and downstream surfaces, with respect to the air stream, of the so arranged catalyst block  70 . In other words, the catalyst heater  73  is so shaped as to sandwich the catalyst block  70  from the front and rear sides thereof. 
   The catalyst block  70  is fitted to an interior wall surface of the upper duct  25 , at a distance secured therefrom, by a metal fitting member  80  shaped as shown in  FIG. 6 . The fitting member  80  is formed by bending sheet metal. The fitting member  80  is composed of a frame portion  81  in the shape of a gate as seen in a front view and anchoring support portions  82  protruding outward from both ends of the frame portion  81 . The frame portion  81  has, along the front-side and rear-side edges thereof, overhanging rims  83  formed so as to bent toward the inside of the frame portion  81 . The overhanging rims  83  prevent the catalyst block  70  inserted in the frame portion  81  from moving frontward or rearward out. The overhanging rims  83  are formed as narrow as possible to minimize the reduction in the vent area of the catalyst block  70 . 
   When the catalyst block  70  is inserted in the frame portion  81  as shown in  FIG. 5 , the top, left-side, and right-side surfaces of the catalyst block  70  make surface contact with the inner surfaces of the frame portion  81 . This state is maintained by cut-out pieces  84  that are cut out of the frame portion  81  so as to protrude in the opposite directions to the anchoring support portions  82 . The cut-out pieces  84  support the bottom surface of the catalyst block  70 , and thus, as shown in  FIG. 5 , the catalyst block  70  is kept at a distance from the surface to which it is fitted. 
   The fitting member  80 , with the catalyst block  70  held therein, is then, as shown in  FIG. 5 , installed inside the upper duct  25  with the anchoring support portions  82  kept in contact with the floor surface (i.e., the upper surface of the ceiling wall  12  of the cooking chamber  11 ) of the upper duct  25 . The anchoring support portions  82  are fastened to the ceiling wall  12  with screws so that the fitting member  80  itself along with the catalyst block  70  is fixed. The fitting member  80  does not make contact with the interior wall surfaces of the upper duct  25  except the one (the upper surface of the ceiling wall  12 ) to which the fitting member is fitted. The catalyst block  70  is held with a gap left from the ceiling wall  12 . 
   The heat generated by the catalyst heater  73  heats not only the catalyst block  70  but also the air stream passing through the upper duct  25 . Thus, the air stream heated by the catalyst heater  73  is further heated by the upper heater  40  so as to reach a desired temperature. 
   Catalyst paint  74  is applied (see  FIG. 1 ) to the interior wall surfaces of the upper duct  25 , starting around the downstream-side end of the catalyst block  70 . The catalyst paint  74  contains, among its coating ingredients, a catalyst that is of the same type or functions in the same way as the one carried by the catalyst block  70 . 
   Also inside the side duct  26 , there are provided a catalyst block and a catalyst heater. As in the upper duct  25 , the side heater  41 , which is the main heat source for producing the hot air stream, is realized with a sheath heater, and part of it is laid near the catalyst block so as to serve as the catalyst heater. The catalyst block in the side duct  26  is fixed by a fitting member similar to the fitting member  80 . The fitting member is fixed to the left inner wall  15 . 
   Catalyst paint similar to that used in the upper duct  25  is applied to the interior wall surfaces of the side duct  26 , starting around the downstream-side end of the catalyst block. 
   In  FIG. 1 , reference number  60  represents foods, and reference number  61  represents a grill that supports foods  60  above a turntable  50 . 
   The cooking oven  1  of the first embodiment operates as follows. When heating cooking is started, air is sucked out of the cooking chamber  11  into the blower  20 , and is sent to the upper duct  25  and the side duct  26 . The air stream that has entered the upper duct  25  is heated by the catalyst heater  73  and the upper heater  40 , and is then, in the form of a hot air stream, blown out through the upper blowout port  30 . The air stream that has entered the side duct  26  is heated by the catalyst heater and the upper heater  41 , and is then, in the form of a hot air stream, blown out through the side blowout port  31 . 
   The heat generated by the catalyst heater  73  and the upper heater  40  heats the catalyst block  70 . The catalyst block  70  is heated, by the radiant heat received from the upstream and downstream sides thereof and the heat carried by the hot air stream passing therethrough, to a temperature (310° C. to 600° C.) at which the catalyst functions satisfactorily. The catalyst paint  74  also is heated, by the radiant heat from the catalyst heater  73  and the upper heater  40  and the heat carried by the hot air stream passing through the inside of the upper duct  25 , to a temperature (200° C. to 400° C.) at which the catalyst functions satisfactorily. Likewise, inside the side duct  26 , the catalyst block and the catalyst paint are heated. 
   The hot air stream blown into the cooking chamber  11  heats foods  60 . As foods  60  are heated, it releases oily fumes and odor substances. The oily fumes and odor substances, mixed with the hot air stream, are sucked through the suction port  32  into the blower  20 , and is then sent out into the upper duct  25  and the side duct  26 . 
   The oily fumes and odor substances that have entered the upper duct  25  are, as they pass through the catalyst block  70 , decomposed into carbon dioxide and water. The oily fumes and odor substances that have passed through the catalyst block  70  without being decomposed and those that have passed through the gap between the catalyst block  70  and the interior wall surfaces of the upper duct  25  flows further through the upper duct  25  toward the upper blowout port  30 , and meanwhile make contact with the catalyst paint  74  so as to be decomposed. Likewise, the oily fumes and odor substances that have entered the side duct  26  are decomposed by the catalyst block and the catalyst paint. 
   Accordingly, the hot air streams that blow out from the upper and side blowout ports  30  and  31  contain greatly reduced amounts of oily fumes and odor substances, and are thus less likely to stain foods  60  or spoil the flavor thereof. Also less soiled are the cooking chamber  11  and the blower  20 . 
   Now, different embodiments of the cooking oven  1  described above will be described. A second to an eleventh embodiment, which will be described below, are all characterized by the shape or structure of the fitting member for the catalyst block  70 , or how it is fitted. The following descriptions assume that the second to eleventh embodiments are applied to the fitting member  80  used in the upper duct  25 , but it should be understood that they are applicable also to the fitting member used in the side duct  26  except in cases where spatial positional relationship matters. 
     FIG. 7  shows a second embodiment. The fitting member  80  is fitted not on the upper surface of the ceiling wall  12  but to the ceiling surface of the upper duct  25 . In this construction, the catalyst block  70 , acted upon by gravitation, spontaneously falls onto the bottom of the frame portion  81  and leaves a gap from the ceiling surface of the upper duct  25 . This makes it possible to omit the cut-out pieces  84 . 
     FIGS. 8 and 9  show a third embodiment. A heater support portion  85  for supporting the bent portion formed at a midpoint of the catalyst heater  73  is formed integrally with one of the anchoring support portions  82  of the fitting member  80 . The heater support portion  85  has an engagement cut  86  formed in an edge thereof so that the catalyst heater  73  is fitted into it. Thus, the heater support portion  85  holds the catalyst heater  73  in such a way that the catalyst heater  73  does not make contact with the catalyst block  70 . 
   As described earlier, the fitting member  80  is made of a metal having a high thermal conductivity. Moreover, the frame portion  81  is kept in surface contact with the top, left-side, and right-side surfaces of the catalyst block  70 . Thus, as shown in  FIG. 9 , the heat generated by the catalyst heater  73  conducts from the heater support portion  85  to the frame portion  81  and then to the catalyst block  70 . This permits the catalyst block  70  to be heated efficiently. 
     FIG. 10  shows a fourth embodiment. The heater support portion  85  is formed in a different part of the fitting member  80 . In the third embodiment, the heater support portion  85  is fitted to, among the pieces that together form the fitting member  80 , the one that is fitted to the upper duct  25 , namely one of the anchoring support portion  82 . This permits the heat conducted from the catalyst heater  73  to readily escape to the walls of the upper duct  25 . To improve this, the heater support portion  85  is formed integrally with the piece that makes surface contract with the side surface of the catalyst block  70 . This permits the heat generated by the catalyst heater  73  to conduct to the catalyst block  70  more efficiently. 
   The fitting member  80  also receives infrared radiation from the catalyst heater  73  and the upper heater  40 . From the perspective of efficient heating of the catalyst block  70 , it is desirable that the fitting member  80  readily absorb radiant heat, i.e., infrared radiation. To this end, the fitting member  80  is used in a form deprived of its inherent metallic luster. 
   Specifically, as the metal material of which the fitting member  80  is made is selected one whose reflectivity lessens or whose color darkens when a certain amount of heat is applied thereto. The color of the fitting member  80  may be changed by application of heat in the process of its being formed, or may be changed as a result of the fitting member  80  being heated as the cooking oven  1  is used. 
   An example of such a metal material is stainless steel SUS304 (a code indicating a particular type of stainless steel according to the Japanese Industrial Standards). This type of steel, as the catalyst block  70  is heated to a temperature (310° C. to 600° C.) at which the catalyst functions satisfactorily, loses the luster inherent in stainless steel and comes to have a different color. It even then maintains resistance to corrosion. Thus, this material is suitable for the purpose of the invention. 
   The infrared absorption coefficient of the fitting member  80  may be further increased by some means. In a fifth embodiment shown in  FIG. 11 , paint of a dark color, such as black, brown, or green, is applied to the fitting member  80 . This permits the fitting member  80  to absorb more radiant heat, and thus helps increase the efficiency with which the catalyst block  70  is heated. The paint does not need to be applied to those portions of the fitting member  80  where it makes surface contact with the catalyst block  70  and with the floor surface of the upper duct  25 . 
     FIGS. 12 and 13  show a sixth embodiment. As in the second embodiment, the fitting member  80  is fitted to the ceiling surface of the upper duct  25 . Here, however, a heat-shielding portion  90  is provided between the anchoring support portions  82  and the upper duct  25 . Although the term “heat-shielding” is used here, it is impossible to completely shield heat in reality. Accordingly, it should be understood that the term “heat-shielding” used here includes the concept of “reducing conduction of heat.” 
   In the sixth embodiment, the heat-shielding portion  90  is realized with projections  91  formed on the anchoring support portions  82 . The projections  91  can be formed by drawing. The contact achieved between the projections  91  and the interior wall surface of the upper duct  25  helps reduce the contact area between the fitting member  80  and the interior wall surface of the upper duct  25 . This limits the conduction of heat from the fitting member  80  to the walls of the upper duct  25 , and thus more of the heat received by the fitting member  80  conducts to the catalyst block  70 . 
   The projections  91  may be formed not on the anchoring support portions  82  but on the upper duct  25 . Alternatively, projections  91  may be formed both on the anchoring support portions  82  and on the upper duct  25  so that they are brought into contact with each other. 
     FIG. 14  shows a seventh embodiment. Also in this embodiment, the fitting member  80  is provided with a heat-shielding portion  90 . In the seventh embodiment, the heat-shielding portion  90  is realized with through holes  92  formed in the vertical portions of the frame portion  81  located just above the anchoring support portions  82 . These through holes  92  help reduce the cross-sectional area there, and thus helps reduce the amount of heat that conducts to the anchoring support portions  82 . 
   Instead of the through holes  92 , cuts may be formed in the edges of the frame portion  81  to serve as the heat-shielding portion  90 . 
     FIG. 15  shows an eighth embodiment. In this embodiment, a catalyst replacement opening  100  is formed in the upper duct  25 , and is covered with a lid  101  from outside the upper duct  25 . The lid  101  is fixed to the upper duct  24  as by being fastened thereto with screws. To the inner surface of this lid  101  is fitted the fitting member  80  with the catalyst block  70  held therein. 
   The lid  101  is formed out of sheet metal, and has a bent portion  102  formed along the edges thereof. The rim of the bent portion  102  makes contact with the upper duct  25 , and thus the area over which the bent portion  102  makes contact with the upper duct  25  is small. That is, the bent portion  102  forms a small-area contact portion interposed between the fitting member  80  and the upper duct  25 , and thus serves as the heat-shielding portion  90 . 
     FIG. 16  shows a ninth embodiment. In this embodiment, the edges of the lid  101  for covering the catalyst replacement opening  100  are formed not into a simply bent portion but into a curled portion  102   a . This also helps reduce the contact area between the upper duct  25  and the lid  101 , and thus serves as the heat-shielding portion  90 . 
     FIG. 17  shows a tenth embodiment. In this embodiment, between the upper duct  25  and the lid  101  is interposed a heat-shielding member  103  to serve as the heat-shielding portion  90 . The heat-shielding member  103  is made of a material having a low thermal conductivity such as heat-resistant resin or ceramic. Using the heat-shielding member  103  helps achieve higher-level heat shielding. 
   Selecting synthetic resin as the material of the heat-shielding member  103  makes it easy to form it into a shape that runs along the contour of the lid  101 . Moreover, it is possible to exploit the elasticity of the synthetic resin to keep airtightness between the upper duct  25  and the lid  101 . 
     FIG. 18  shows an eleventh embodiment. In this embodiment, highly elastic synthetic resin is selected as the heat-shielding member. This synthetic resin is formed into a shape having a C-shaped cross section and is fitted around the lid  101  to form a heat-shielding member  103   a  having a sealing capability. This makes it possible to permit a single member to serve both as the heat-shielding portion  90  and to keep airtightness. 
   The embodiments starting with the eighth shown in  FIG. 15  and ending with the eleventh shown in  FIG. 18  all relate to the structure of the heat-shielding portion  90  as used in constructions in which the fitting member  80  for the catalyst block  70  is fitted to the lid  101  for covering the catalyst replacement opening  100 . A similarly structured heat-shielding portion  90  may be fitted to a fitting member  80  that is fitted directly to an interior wall surface of the upper duct  25  without a lid  101  interposed in between. 
     FIGS. 19 to 25  show a twelfth to a fifteenth embodiment, respectively. The twelfth to fifteenth embodiments all relate to the catalyst paint applied inside a duct. Although the upper duct  25  is illustrated as the target to which these embodiments are applied, it should be understood that they are equally applicable to the side duct  26 . 
     FIG. 19  shows a twelfth embodiment of the cooking oven  1 . In this embodiment, one of the interior wall surfaces of the upper duct  25 , i.e., the one that does not form the ceiling wall  12  of the cooking chamber  11 , is formed into an irregular surface  75 . The catalyst paint  74  is applied to the irregular surface  75 , and thus the surface, even with the same area as seen in a plan view, makes contact with the air stream over a larger effective area. This helps enhance the decomposition performance of the catalyst paint  74  as a whole. Instead of forming only the interior wall surface opposite to the ceiling wall  12  into a irregular surface  75 , it is also possible, and more preferable, to form all the four interior wall surfaces of the upper duct  25  into irregular surfaces and apply the catalyst paint  74  thereto. Likewise, the interior wall surfaces of the side duct  26  are formed into irregular surfaces, and the catalyst paint  74  is applied thereto. 
   An irregular surface  75  can be formed by forming a large number of dimples on an interior wall surface of a duct or by bonding thereto a sheet having punched holes or laths formed thereon. 
     FIGS. 20 and 21  show a thirteenth embodiment of the cooking oven  1 . In this embodiment, the surface irregularities on an interior wall surface of the upper duct  25  are formed as follows. An irregular surface  75  has wave-shaped irregularities composed of slanted surfaces  75   a  that face in the direction from which the air stream blows and slanted surfaces  75   b  that face in the direction opposite thereto. When the length L 1  of the slanted surfaces  75   a  is compared with the length L 2  of the slanted surfaces  75   b , the length L 1  is long, and the length L 2  is short. Since the slanted surfaces  75   a , with which the air stream collides, are longer, the catalyst paint  74  as a whole exerts still higher decomposition performance. All the four interior wall surfaces of the upper duct  25  may be formed into irregular surfaces  75 . A similar structure may be applied to an interior wall surface of the side duct  26 . 
     FIGS. 22 and 23  show a fourteenth embodiment of the cooking oven  1 . In the cooking oven  1  of the fourteenth embodiment, to increase the area of the catalyst paint surface, ridge-shaped or groove-shaped irregularities are formed along the air stream inside the upper duct  25 . To this end, a corrugate plate  76  is fixed to an interior wall surface of the upper duct  25 . The corrugate plate  76  has a cross-sectional shape as shown in  FIG. 23  so as to have grooves  76   b  between triangular ridges  76   a . The grooves  76   b  are formed on both sides of the corrugate plate  76 . 
   The corrugate plate  76  is made of metal, and has catalyst paint applied on both sides thereof. Catalyst paint is applied also to the part of an interior wall surface of the upper duct  25  located on the downstream side of the catalyst block  70 , and the corrugate plate  76 , having the catalyst paint already applied thereto, is fixed to that interior wall surface as by being fastened with screws. 
   In this construction, the catalyst paint surface has an increased area. Moreover, since the ridges  76   a  or grooves  76   b  run along the air stream, they do not diminish the flow speed of the air stream. This makes it possible to send the hot air stream efficiently while keeping it in contact with the catalyst paint. The side duct  26  is given a similar structure. 
     FIG. 24  shows a fifteenth embodiment of the cooking oven  1 . In this embodiment, instead of the corrugate plate  76 , an extruded member  77  provided with a large number of parallel fins  77   a  is used. Between the parallel fins  77   a  are formed grooves  77   b  through which the air stream passes. The extruded member  77  is made of metal, and is fixed, as by being fastened with screws, to the portion of an interior wall of the upper duct  25  located on the downstream side of the catalyst block  70 . Then, catalyst paint is applied to the interior wall surface of the upper duct  25  including the extruded member  77 . 
   Also in this construction, the catalyst paint surface has an increased area. Moreover, since the parallel fins  77   a  and the grooves  77   b  between them run along the air stream, they do not diminish the flow speed of the air stream. This makes it possible to send the hot air stream efficiently while keeping it in contact with the catalyst paint. The side duct  26  is given a similar structure. 
     FIG. 25  shows a sixteenth embodiment of the cooking oven  1 . In the cooking oven  1  of the sixteenth embodiment, inside the upper duct  25 , there is provided a air-stream-regulating plate  78  for directing the air stream in the direction of the upper blowout port  30  and simultaneously regulating the air stream. Catalyst paint  74  is applied to an interior wall surface of the upper duct  25  including the air-stream-regulating plate  78 . 
   Also in this construction, the catalyst paint surface has an increased area. Moreover, since the air stream is surely kept in contact with the air-stream-regulating plate  78 , the catalyst paint  74  surely functions satisfactorily. The side duct  26  is given a similar structure. 
     FIGS. 26 ,  27 , and  28  show a seventeenth embodiment of the cooking oven  1 . 
   When the fan  22  sucks in air out of the cooking chamber  11 , fine particles of oil released from foods  60 , together with the air, enters the fan casing  21 . Most of the oil that has entered is then sent, together with the air, into the upper duct  25  or the side duct  26 , and is decomposed by the catalyst. However, part of the oil, while passing through the fan casing  21 , settles on the interior wall surfaces thereof. As time passes, more and more oil settles on the interior wall surfaces of the fan casing  21  until the oil, in the form of oil drips, starts to flow down the wall surfaces. This oil flows through an oil drain hole  21   b  into the cooking chamber  11 . On an occasion of cleaning, the oil is wiped off along with the oil that has settled on the interior surfaces of the cooking chamber  11 . 
   Air flows through the inside of the upper duct  25  and of the side duct  26 . Suppose that there is a grid across a cross-section of the duct, and compare the amounts of air stream that flow through the individual squares of the grid. Then, the amounts of air stream that flow through different squares are not equal, but larger amounts of air stream pass through some squares than through others. 
   When the duct is curved or bent, the air flowing therethrough is acted upon by centrifugal force. This causes an increasingly large amount of air, and thus an increasingly large amount of air stream, to flow through an increasingly outward part of the curve or bend. This tendency persists even after the air has exited from the curve or bend and entered a straight path, and accordingly an increasingly large amount of air stream flows through the part of the straight path that is contiguous with an increasingly outward part of the curve or bend. 
   According to the present invention, from this perspective, the arrangement of the heaters and the catalyst blocks is ingeniously worked out. 
   First, a description will be given of the heaters. The upper heater  40  and the side heater  41  are each a sheath heater, and are arranged so as to describe a complicatedly bent shape across a cross-section of the upper duct  25  and the side duct  26 , respectively. The main portions of those sheath heaters, i.e., those portions thereof where they generate a large amount of heat, are laid in a ceiling-side portion inside the upper duct  25  (see  FIG. 26 ) and in a left-side portion, as seen from the front, inside the side duct  26  (see  FIG. 27 ), respectively. 
   As shown in  FIG. 26 , the upper duct  25  is bent in a portion thereof that connects to the upper discharge port  23  of the fan casing  21 , and the upper heater  40  is arranged on the downstream side of this bent portion. The distribution of the amount of air stream within a cross section of the upper duct  25  is such that more air stream flows through a more outward, i.e., closer to the ceiling, part of the bent portion. The distribution of the amount of heat generated by the upper heater  40  is adjusted to this distribution of the amount of air stream, specifically in such a way that more heat is generated in a part where more air stream flows, and the heater is so shaped as to meet that requirement. As a result, different parts of the air flowing through a cross section of the duct receive, according to the amount of air stream that flows there, commensurate amounts of heat, achieving efficient heating of air. 
   With respect to the side duct  26 , as shown in  FIG. 27 , it is bent in a portion thereof that connects to the side discharge port  24  of the fan casing  21 , and the side heater  41  is arranged on the downstream side of this bent portion. Thus, the distribution of the amount of air stream within a cross section of the side duct  26  is such that more air stream flows through a more outward, i.e., more leftward as seen from the front, part of the bent portion. The distribution of the amount of heat generated by the side heater  41  is adjusted to this distribution of the amount of air stream, specifically in such a way that more heat is generated in a part where more air stream flows, and the heater is so shaped as to meet that requirement. As a result, different parts of the air flowing through a cross section of the duct receive, according to the amount of air stream that flows there, commensurate amounts of heat, achieving efficient heating of air. 
   The catalyst block  70  is arranged lopsided toward that side of a cross section of the duct at which a larger amount of heat is generated. Specifically, in the upper duct  25 , the catalyst block  70  is fitted to the ceiling wall thereof, and, in the side duct  26 , the catalyst block  70  is fitted to the left-hand interior side wall thereof as seen from the front. 
   The fitting member  80  having the catalyst block  70  held therein is fastened, in the upper duct  25 , to the ceiling wall thereof with screws and, in the side duct  26 , to the left-hand interior side wall thereof, as seen from the front, with screws. 
   In this way, the catalyst block  70  is fitted to that one of the duct interior walls (of which the ceiling wall is one) which is located where the upper heater  40  or side heater  41  generates a larger amount of heat. As a result, as well as with directly radiated heat, with the heat conducted through the duct walls, the catalyst block is heated efficiently. 
     FIGS. 29 and 30  show an eighteenth embodiment of the cooking oven  1 . In the eighteenth embodiment, a modification is made in the structure of the side duct  26 . This embodiment can be implemented on the basis of any of the embodiments already described. 
   Through the side duct  26  flow oily fumes containing oil, fat, odor substances, and the like released from foods  60 . Some kinds of food  60  release a large amount of oily fumes. When an extremely large amount of oily fumes is released, the oil that has not been decomposed by the catalyst soils the interior surfaces of the side duct  26 , and collects at the bottom thereof. Also as the cooking oven  1  is used for a long period, oil gradually collects. 
   To overcome these inconveniences, the floor surface  26   a  of the side duct  26  is so slanted as to sink toward the cooking chamber  11 . In the left inner wall  15  of the cooking chamber  11 , a plurality of oil drain holes  110  that lead to the lowest part of the floor surface  26  are formed at predetermined intervals along the depth direction of the side duct  26 . 
   In this construction, oil that has flown down to the bottom of the side duct  26  flows along the slanted floor surface  26   a , and then flows through the oil drain holes  110  into the cooking chamber  11 . The oil that has flown into the cooking chamber  11  can be easily wiped off and thereby disposed of. This prevents oil from remaining on the catalyst paint surface inside the side duct  26 , and thus helps maintain the effect of the catalyst paint without deterioration. 
     FIG. 31  shows a nineteenth embodiment of the cooking oven  1 . The nineteenth embodiment is a modified version of the eighteenth embodiment. In this embodiment, in the front face of the cooking oven  1 , there is formed a rectangular opening  111  that leads to the bottom of the side duct  26 . Through this opening  111 , a drawer-type drain pan  112  is inserted into the side duct  26 . The drain pan  112  is open toward the cooking chamber  11 , and has the floor surface  113  thereof slanted so as to sink toward the cooking chamber  11 . In the left inner wall  15  of the cooking chamber  11 , a plurality of oil drain holes  110  that lead to the lowest part of the floor surface  113  are formed at predetermined intervals along the depth direction of the side duct  26 . 
   In this construction, oil that has flown down to the bottom of the side duct  26  flows along the slanted floor surface  113  of the drain pan  112 , and then flows through the oil drain holes  110  into the cooking chamber  11 . The oil that has flown into the cooking chamber  11  can be easily wiped off and thereby disposed of. This prevents oil from remaining on the catalyst paint surface inside the side duct  26 , and thus helps maintain the effect of the catalyst paint without deterioration. 
   When the drain pan  112  becomes soiled, it is drawn out by pulling a knob  114  fitted to the front face thereof. The drain pan  112  is cleaned with detergent or the like, and is then put back into the bottom of the side duct  26 . 
     FIG. 32  shows a twentieth embodiment of the cooking oven  1 . In the twentieth embodiment, a modification is made in the drain pan  112  of the nineteenth embodiment. Specifically, in the drain pan  112  of the twentieth embodiment, oil collects in a gutter-shaped oil collection portion  115 . Accordingly, no oil drain holes are formed in the left inner wall  15  of the cooking chamber  11 . When oil collects in the oil collection portion  115 , the drain pan  112  is drawn out by pulling a knob  114  fitted to the front face thereof, and the oil is disposed of. The drain pan  112  is cleaned with detergent or the like, and is then put back into the bottom of the side duct  26 . 
   Advisably, the interior shape of the side duct  26  and the shape of the catalyst paint surface are so devised as to permit easy collection of oil in the drain pan  112 . This applies also to the nineteenth embodiment. 
   A mechanism for oil disposal as described above may be provided also for the upper duct  25 . To permit oil to flow into the cooking chamber  11 , the floor surface of the upper duct  25  is slanted as follows. It is so slanted as to one-sidedly sink toward one of the rear inner wall  14 , left inner wall  15 , and right inner wall  16 ; alternatively, like a gable roof, it is so slanted as to two-sidedly sink toward both the left inner wall  15  and right inner wall  16 ; or alternatively, like a hipped roof, it is so slanted as to three-sidedly sink toward the rear inner wall  14 , left inner wall  15 , and right inner wall  16 . In any case, oil drain holes are formed as close as possible to the rear inner wall  14 , left inner wall  15 , and right inner wall  16  so that oil does not drip onto foods  60 . Consideration needs to be taken also to prevent entry of oil into the blower  20 . 
   A drain pan like the drain pan  112  used in the nineteenth and twentieth embodiments may be provided for the upper duct  25 . 
   In a case where a drain pan is provided for the upper duct  25  or side duct  26 , the position in which to arrange the drain pan, the shape and fitting arrangement of the door  17  should advisably be so designed that the drain pan can be drawn out when the door  17  is open. 
   The embodiments described hereinbefore all deal with cases in which catalyst paint is applied to an interior wall surface of a duct through which a hot air stream for heating foods is passed, i.e., a duct that forms a principal circulation passage. It is, however, also possible to provide a subsidiary circulation passage through which the air inside a cooking chamber is circulated for the purpose of decomposing oil fumes and odor substances rather than for the purpose of heating foods, and apply catalyst paint to an interior wall surface of a duct that forms the subsidiary circulation path. 
   A catalyst block does not necessarily have to be used in combination with catalyst paint. That is, it is also possible to rely solely on catalyst paint. 
   It should be understood that the embodiments of the present invention described hereinbefore are merely examples of constructions according to the invention, and are not meant to limit the scope of the invention in any way; that is, many further modifications and variations are possible in carrying out the invention within the concept of the invention. 
   INDUSTRIAL APPLICABILITY 
   As described above, according to the present invention, in a cooking oven wherein a catalyst is made to act upon a hot air stream circulated inside a cooking chamber in order to decompose oily fumes and odor substances, it is possible to efficiently heat the catalyst to make it function satisfactorily. Moreover, it is possible to arrange the catalyst easily. Furthermore, in arranging a heater inside a duct through which a air stream is sent to the cooking chamber, it is possible to improve the air heating efficiency of the heater. With these features, it is possible to enhance the cooking performance of professional-use and household-use cooking ovens.