Abstract:
A portable wireless device wherein antenna performance deterioration when using a slide mechanism having a metal member can be prevented. In this portable wireless device, a second housing ( 102 ) is slidably attached to a first housing ( 101 ). The circuit board ( 105 ) is provided in the first housing ( 101 ) and has a slit ( 110 ) which extends in a direction crossing the sliding direction of the first housing ( 101 ) and is located below a power feed unit ( 109 ) when the wireless device is opened. The circuit board ( 108 ) is provided in the second housing ( 102 ) and overlaps with the bottom side of the circuit board ( 105 ) as seen from a plan view when the first housing ( 101 ) is slid open. The antenna ( 107 ) is provided on the upper side of the second housing ( 102 ). The power feed unit ( 109 ) supplies power to the antenna ( 107 ) at a position close to the antenna ( 107 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a portable radio device. More particularly, the present invention relates to a portable radio device in which multiple casings are connected with each other in a slidable fashion and are placed in an open state and a closed state following slide operations. 
       BACKGROUND ART 
       [0002]    Conventionally, a portable radio device in which an upper casing and a lower casing are connected in a mutually slidable fashion is known. When this slide portable radio device is placed in an open state, the circuit board of the upper casing and the circuit board of the lower casing partly overlap on top of each other. Also, with a slide portable radio device, each circuit board and a metallic slide component to guide the slide operations of the casings are placed close to each other. Thus, in a conventional slide portable radio device, the circuit board of the upper casing and the circuit board of the lower casing are electromagnetically coupled through a slide component. As a result of this, a conventional slide portable radio device has a problem that, if an antenna is placed in the upper end side of the lower casing and a power feeding section is also located in the upper end side of the lower casing, the current traveling in the circuit board of the upper casing has the opposite phase to the antenna current traveling in the circuit board of the lower casing towards a power feeding section, so that antenna performance is degraded. This kind of problem does not occur in a flip portable radio device in which the circuit board of the upper casing and the circuit board of the lower casing do not overlap one above the other in an open state, and therefore is specific to a slide portable radio device. 
         [0003]    To solve the above problem, a method of placing an antenna in the lower end side of the lower casing to allow an antenna current which has the same phase as the current travelling in the circuit board of the upper casing to travel in the circuit board of the lower casing is possible (for example, patent literature  1 ), or a method of forming a slide mechanism component with an insulating resin is possible. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1
   Japanese Patent Application Laid-Open No. 2006-217572   
 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    However, there is a problem that if an antenna is provided in the lower end side of the lower casing, generally, the lower end side of the lower casing is a part held by a human hand, for example, during a call, so that a human hand becomes a dielectric and degrades antenna performance. Also, there is a problem that, if a slide mechanism component is formed with a resin, compared to the case of forming a slide mechanism component with metal, the mechanical strength becomes low and provides a factor of failure. 
         [0007]    It is therefore an object of the present invention to provide a portable radio device that can prevent antenna performance degradation when a slide mechanism using a metal member is provided. 
       Solution to Problem 
       [0008]    The portable radio device according to the present invention employs a configuration having: a first casing; a second casing that is slidably attached to the first casing; a first circuit board that is provided in the first casing; a second circuit board that is provided in the second casing and that overlaps with a lower side of the first circuit board in a plan view when the first casing slides into an open state; an antenna that is provided in an upper side of the second casing; and a power feeding section that is provided near the antenna and that feeds power to the antenna, and, in this portable radio device, the first circuit board has an insulation section that extends in a direction to cross a slide direction of the first casing and that is located lower than the power feeding section in the open state. 
         [0009]    The portable radio device of the present invention employs a configuration having: a first casing; a second casing that is slidably attached to the first casing; a metal section that is flat and that is provide in the first casing; a circuit board that is provided in the second casing and that overlaps with a lower side of the metal section in a plan view when the first casing slides into an open state; an antenna that is provided in an upper side of the second casing; and a power feeding section that is provided near the antenna and that feeds power to the antenna, and, in this portable radio device, the metal section has an insulation section that extends in a direction to cross a slide direction of the first casing and that is located lower than the power feeding section in the open state. 
         [0010]    The portable radio device according to the present invention employs a configuration having: a first casing; a second casing that is slidably attached to the first casing; a first circuit board that is provided in the first casing; a second circuit board that is provided in the first casing; a signal wire that connects the first circuit board and the second circuit board; a third circuit board that is provided in the second casing and that overlaps with the second circuit board in a plan view when the first casing slides into an open state; an antenna that is provided in an upper side of the second casing; and a power feeding section that is provided near the antenna and that feeds power to the antenna, and, in this portable radio device, the first circuit board, the second circuit board, and the signal wire form a slit; and the slit has a lengthwise direction that crosses a slide direction of the first casing, and is located lower than the power feeding section in the open state. 
       Advantageous Effects of Invention 
       [0011]    The present invention can prevent antenna performance degradation when a slide mechanism using a metal member is provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side view of a portable radio device according to embodiment 1 of the present invention in an open state; 
           [0013]      FIG. 2  is a side view of a portable radio device according to embodiment 1 of the present invention in a closed state; 
           [0014]      FIG. 3  is a plan view of the first casing according to embodiment 1 of the present invention; 
           [0015]      FIG. 4  is a plan view of the circuit board according to embodiment 2 of the present invention; 
           [0016]      FIG. 5  is a side view of a portable radio device according to embodiment 3 of the present invention in an open state; 
           [0017]      FIG. 6  is a side view of a portable radio device according to embodiment 4 of the present invention in an open state; 
           [0018]      FIG. 7  is a plan view of the first casing according to embodiment 5 of the present invention; 
           [0019]      FIG. 8  is a plan view of the first casing showing another example of the circuit board according to embodiment 5 of the present invention; 
           [0020]      FIG. 9  is a plan view of the first casing showing yet another example of the circuit board according to embodiment 5 of the present invention; 
           [0021]      FIG. 10  is a plan view of the first casing showing yet another example of the circuit board according to embodiment 5 of the present invention; 
           [0022]      FIG. 11  is a plan view of the first casing according to embodiment 6 of the present invention; 
           [0023]      FIG. 12  is a plan view of the first casing showing another example of the first casing according to embodiment 6 of the present invention; 
           [0024]      FIG. 13  is a plan view of the first casing according to embodiment 7 of the present invention; 
           [0025]      FIG. 14  is a plan view of the first casing showing another example of the first casing according to embodiment 7 of the present invention; 
           [0026]      FIG. 15  is a plan view of the first casing according to embodiment 8 of the present invention; 
           [0027]      FIG. 16  is a plan view of the first casing showing another example of the first casing according to embodiment 8 of the present invention; 
           [0028]      FIG. 17  is a side view of a portable radio device according to embodiment 9 of the present invention in an open state; 
           [0029]      FIG. 18  is a plan view of a metal section according to embodiment 9 of the present invention; 
           [0030]      FIG. 19  is a plan view of a metal section showing another example of a metal section according to embodiment 9 of the present invention; 
           [0031]      FIG. 20  is a plan view of a metal section showing yet another example of a metal section according to embodiment 9 of the present invention; 
           [0032]      FIG. 21  is a plan view of the first casing showing another example of the circuit board; and 
           [0033]      FIG. 22  is a plan view of the first casing showing another example of a slit provided in the circuit board. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0034]    Now, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0035]      FIG. 1  is a side view of portable radio device  100  according to the embodiment 1 of the present invention in an open state.  FIG. 2  is a side view of portable radio device  100  according to the embodiment 1 of the present invention in a closed state. 
         [0036]    Portable radio device  100  is mainly formed with first casing  101 , second casing  102 , first slide mechanism section  103 , second slide mechanism section  104 , circuit board  105 , display section  106 , antenna  107 , circuit board  108 , and power feeding section  109 . 
         [0037]    First casing  101  is formed in a rectangular shape in a plan view and is slidably attached to second casing  102  to switch from the open state of  FIG. 1  to the closed state of  FIG. 2  or to switch from the closed state of  FIG. 2  to the open state of  FIG. 1 , by sliding with first slide mechanism section  103 . Thus, first casing  101  is attached to second casing  102  to be able to slide along the lengthwise direction of first casing  101  (a vertical direction in  FIG. 1  and  FIG. 2 ). In the open state of  FIG. 1 , by sliding with first slide mechanism section  103  that is bent to erect, first casing  101  is held on second casing  102  in an erect state. First casing  101  has circuit board  105  and display section  106 . 
         [0038]    Second casing  102  is formed in a rectangular shape in a plan view and is slidably attached to first casing  101  to switch from the open state of  FIG. 1  to the closed state of  FIG. 2  or to switch from the closed state of  FIG. 2  to the open state of  FIG. 1 , by sliding with first slide mechanism section  104 . Also, second casing  102  has second slide mechanism section  104  and circuit board  108 . Second casing  102  has antenna  107  in the upper end part (the upper end part of  FIG. 1  and  FIG. 2 ). In an open state, second casing  102  holds first casing  101  in an erect state as shown in  FIG. 1 , and overlaps with first casing  101  in a closed state as shown in  FIG. 2 . 
         [0039]    First slide mechanism section  103  is formed by bending a metal plate. Also, first slide mechanism section  103  slides in a vertical direction in  FIG. 1  and  FIG. 2 , guided by a rail (not shown) provided in second slide mechanism section  104 . First slide mechanism section  103  is attached to first casing  101  and slides with first casing  101 . By sliding along a bent and erect shape guided by second slide mechanism section  104 , in an open state, first slide mechanism section  103  holds first casing  101  in an erect state with respect to second casing  102 . 
         [0040]    Second slide mechanism section  104  is made from a metal plate, is attached to second casing  102 , and slides with second casing  102 . Second slide mechanism section  104  has a rail (not shown) to guide the slide operations of first slide mechanism section  103 . 
         [0041]    Circuit board  105  is provided in first casing  101  and display section  106  such as LCD is attached. Circuit board  105  has slit  110  extending from one end in a perpendicular direction to a slide direction (a horizontal direction in  FIG. 1  and  FIG. 2 ) of first casing  101  and penetrating circuit board  105  in a thickness direction. When first casing  101  and second casing  102  are in an open state, slit  110  is located lower (lower than broken line P 1  in  FIG. 1 ) than antenna  107  and power feeding section  109 . Here, slit  110  is provided to suppress the current to travel below slit  110  in circuit board  105  in  FIG. 1 . Thus, a “slit” is not mandatory, and, as long as an insulation section is provided, it is possible to achieve the effect of the present embodiment. With the present embodiment, a case will be described where slit  110  is provided as one example of an insulation section. The details of slit  110  will be described later. 
         [0042]    Display section  106  is, for example, a liquid crystal display apparatus (LCD) and is attached to circuit board  105 . Display section  106  shows, for example, image data that portable radio device  100  receives. 
         [0043]    By being attached above circuit board  108 , antenna  107  is provided in an upper part of second casing  102 . By this means, when the lower side of second casing  102  is held by a human hand, antenna performance degradation caused by the hand can be prevented. Antenna  107  is fed power from power feeding section  109 . 
         [0044]    Circuit board  108  is provided in second casing  102 , and antenna  107  and power feeding section  109  are provided in its upper end part. In the open state of  FIG. 1 , on a plan view, the upper side of circuit board  108  overlaps, with the lower side of circuit board  105  (part between broken line P 1  and broken line P 2  in  FIG. 1 ). 
         [0045]    Power feeding section  109  is provided above circuit board  108  and feeds power to antenna  107 . Power feeding section  109  does not have to be provided in circuit board  108  and can be provided in an arbitrary location around antenna  107 . 
         [0046]    Next, slit  110  provided in circuit board  105  will be described using  FIG. 3 .  FIG. 3  is a plan view of first casing  101 . 
         [0047]    On a plan view, circuit board  105  is provided almost over the entire surface of first casing  101 . In circuit board  105 , slit  110  is formed from one end part  301  of circuit board  105  in a perpendicular direction to a slide direction (a vertical direction in  FIG. 3 ) of first casing  101 . Also, in circuit board  105 , over slit  110 , display section  106  is provided in an upper part (an upper part in  FIG. 3 ), and operation key section  303  is provided in a lower part (a lower part in  FIG. 3 ). In narrow section  304  of circuit board  105 , circuit patterns (not shown) are formed to transmit the signals input from operation key section  303 , to a signal processing section such as a CPU (not shown) mounted on circuit board  105 . 
         [0048]    Slit  110  is a through hole that is formed in circuit board  105  and that penetrates circuit board  105  in a thickness direction (a perpendicular direction to the sheet of  FIG. 3 ). The length of width r 1  (see  FIG. 3 ) from end part  301  of slit  110  is determined such that the perimeter of the lower side of slit  110  in circuit board  105  is half-wavelength (λ/2) of the frequency used by portable radio device  100 . The higher the frequency used by portable radio device  100 , the smaller the perimeter below slit  110  in circuit board  105  is placed. Here, the perimeter below slit  110  in circuit board  105  is referred to the length ( 11  in  FIG. 3 ) along slit  110 , end parts  301 ,  300 , and  302  of circuit board  105 , in area r 2  below slit  110  in circuit board  105 . 
         [0049]    Operation key section  303  has contact point patterns  303   a - 303   e.  Operation key section  303  has contact point patterns  303   a - 303   e  to be electrically connected when multiple operation keys (not shown) provided in first casing  101  are pressed. 
         [0050]    Contact point patterns  303   a - 303   e  electrically connect with the conductive movable contact points provided in the operation keys when the operation keys (not shown) provided in first casing  101  are pressed. Contact point patterns  303   a - 303   e  electrically connect with circuit patterns (not shown) connected to a signal processing section (not shown) provided on circuit board  105 . By this means, for example, when one operation key is pressed, multiple contact point patterns  303   a - 303   e  are connected with the movable contact point provided in the pressed operation key, are placed in an electrically conducting state (ON) with respect to each other, and therefore transmit an ON signal to a signal processing section through the circuit patterns. On the other hand, when the press of one operation key is released, multiple contact point patterns  303   a - 303   e  are disconnected from the movable contact point provided in the operation key where the press is released, are placed in an electrically non-conducting state (OFF) with respect to each other, and therefore transmit an OFF signal to a signal processing section through the circuit patterns. 
         [0051]    In fact, generally, the signals output from each contact point patterns  303   a - 303   e  of operation key section  303  are two kinds of signals, ON and OFF, so that the circuit configuration in operation key section  303  is simpler than a circuit configuration, for example, in IC having multiple input-output terminals. 
         [0052]    Next, the reason antenna performance of antenna  107  is not degraded in portable radio device  100  having the above configuration will be explained. 
         [0053]    As conventionally known, in the open state of  FIG. 1 , circuit board  105  and circuit board  108  are electrically connected at the part (part between P 1  and P 2 ) where circuit board  105  and circuit board  108  overlap one above the other, through first slide mechanism section  103  and second slide mechanism section  104 . However, the present embodiment provides slit  110 to electrically disconnect area r 2  below slit  110  in circuit board  105 , and suppresses the current transmitting in area r 2  below slit  110  in circuit board  105 . Thus, although conventionally in area r 2 , the current transmits in the direction to cancel antenna current transmitting on circuit board  108  upward in  FIG. 1  towards power feeding section  109  in antenna  107 , the present embodiment provides slit  100  to suppress the current transmitting in area r 2 . By this means, the present embodiment can prevent antenna performance degradation of antenna  107 . 
         [0054]    Therefore, the present embodiment provides, in a circuit board provided in the first casing, a slit that is located lower than a power feeding section in an open state, so that it is possible to electrically disconnect the part of the circuit board below the slit, and to prevent antenna performance degradation when a slide mechanism using a metal member is provided. The present embodiment provides an operation key section having a simple configuration below the slit provided in the circuit board, so that it is possible to provide the circuit patterns in a narrow area that is created by providing the slit. With the circuit board provided in the first casing, the present embodiment suppresses the current transmitting in the area below the slit and also provides an operation key section in the area below the slit, so that it is possible to reduce the influence to the antenna current caused by a hand operating the operation key section. 
         [0055]    Although with the present embodiment a slit is formed from one end part of a circuit board, the present embodiment is not limited to this, and it is equally possible to form a slit that extends from any arbitrary location in the circuit board. 
       Embodiment 2 
       [0056]      FIG. 4  is a plan view showing circuit board  401  according to embodiment 2 of the present invention. 
         [0057]    Compared to circuit board  105  according to embodiment 1 shown in  FIG. 3 , circuit board  401  shown in  FIG. 4  adds reactance element  402 . Also, parts in  FIG. 4  that are the same as in  FIG. 3  will be assigned the same reference numerals as in  FIG. 3  and overlapping descriptions will be omitted. Also, the portable radio device of the present embodiment has the same configuration as the above embodiment 1 except that circuit board  401  is provided instead of circuit board  105 , so that the overlapping descriptions will be omitted. Also,  FIG. 4  will be described using the reference numerals of  FIG. 1  except for circuit board  401 . 
         [0058]    On a plan view, circuit board  401  is provided almost over the entire surface of first casing  101  in a plan view. In circuit board  401 , slit  110  is formed from one end part  301  of circuit board  105  in a perpendicular direction to a slide direction (a vertical direction in  FIG. 4 ) of first casing  101 . Also, in circuit board  401 , over slit  110 , display section  106  is provided in an upper part (an upper part in  FIG. 4 ), and operation key section  303  is provided in a lower part (a lower part in  FIG. 4 ). In narrow section  304  of circuit board  401 , circuit patterns (not shown) are formed to transmit the signals input from operation key section  303 , to a signal processing section such as a CPU (not shown) mounted on circuit board  105 . In circuit board  401 , reactance element  402  that connects end part  405  and end part  406  forming slit  110  and opposing each other is provided. 
         [0059]    Reactance element  402  electrically connects between end part  405  and end part  406  forming slit  110  in circuit board  401  and opposing each other, and adjusts the electrical length of an antenna. Specifically, reactance element  402  electrically connects the ground part of end part  405  and the ground part of end part  406 , and consequently adjusts the electrical length of antenna  107  in circuit board  401 . 
         [0060]    Therefore, besides the above effect of embodiment 1, the present embodiment electrically connects between end parts forming a slit in a circuit board and opposing each other, by means of a reactance element, and consequently can achieve optimal antenna performance in the desired frequency. Especially, if the portable radio device is multiband-compatible, a reactance element adjusts the electrical length, and consequently the portable radio device can achieve optimal antenna performance in each band. 
         [0061]    Although with the present embodiment a slit is formed from one end part of a circuit board, the present embodiment is not limited to this, and it is equally possible to form a slit that extends from any arbitrary location in the circuit board. 
       Embodiment 3 
       [0062]      FIG. 5  is a side view of portable radio device  500  according to the embodiment 3 of the present invention in an open state. 
         [0063]    Compared to portable radio device  100  according to embodiment 1 shown in  FIG. 1 , portable radio device  500  shown in  FIG. 5  adds cable  501 . Also, parts in  FIG. 5  that are the same as in  FIG. 1  will be assigned the same reference numerals as in  FIG. 1  and overlapping descriptions will be omitted. 
         [0064]    Portable radio device  500  is mainly formed by first casing  101 , second casing  102 , first slide mechanism section  103 , second slide mechanism section  104 , circuit board  105 , display section  106 , antenna  107 , circuit board  108 , power feeding section  109 , and cable  501 . 
         [0065]    Circuit board  105  is provided in first casing  101  and display section  106  such as LCD is attached. Circuit board  105  has slit  110  extending from one end in a perpendicular direction to a slide direction (a vertical direction in  FIG. 5 ) of first casing  101  and penetrates circuit board  105  in a thickness direction. When first casing  101  and second casing  102  are in an open state, slit  110  is located lower (lower than broken line P 1  in  FIG. 5 ) than antenna  107  and power feeding section  109 . Above slit  110 , the ground part of circuit board  105  is electrically connected with the ground part of circuit board  108  by means of cable  501 . A “slit” is not mandatory, and, as the above embodiment 1, as long as an insulation section is provided, it is possible to gain the effect of the present embodiment. 
         [0066]    Circuit board  108  is provided in second casing  102 , and antenna  107  and power feeding section  109  are provided in its upper end part. The ground part of circuit board  108  is electrically connected with the ground part of circuit board  105  by means of cable  501 . 
         [0067]    Cable  501  is, for example, a flexible cable (FPC), and transmits a signal received and processed in a radio circuit (not shown) provided in circuit board  108  to, for example, display section  106  provided in circuit board  105 . Also, cable  501  electrically connects the ground part of circuit board  105  and the ground part of circuit board  108 . In this case, cable  501  connects with the ground part of circuit board  105  above slit  110 . 
         [0068]    Next, the flow of antenna current in portable radio device  500  will be described. 
         [0069]    In the ground part of circuit board  108  in portable radio device  500 , antenna current e 1  transmits toward power feeding section  109 , that is, upward in  FIG. 5 . The ground part of circuit board  105  and the ground part of circuit board  108  are electrically connected by cable  501 , and therefore antenna current e 2  transmits upward in  FIG. 5  in the ground part of circuit board  105 . Thus, antenna current e 2  transmitting in circuit board  105  transmits in the same direction as antenna current e 1  transmitting in circuit board  108 , and consequently can be regarded as an extension of antenna current e 1  transmitting in circuit board  108 . On the other hand, the ground part of circuit board  105  provides slit  110  to suppress the current transmitting downward in  FIG. 5 . By this means, antenna  107 , circuit board  105 , circuit board  108 , and power feeding section  109  can form an antenna. 
         [0070]    In fact, conventionally, in circuit board  105 , the current transmits in the direction to cancel antenna current e 1  of circuit board  108 , so that, if cable  501  connects the ground part of circuit board  105  and the ground part of circuit board  108 , the current transmitting in the direction to cancel antenna current e 1  is increased. Thus, conventionally, it has been difficult to use the ground part of circuit board  105  as an antenna. On the other hand, circuit board  105  of the present embodiment provides slit  110  to suppress the current transmitting in the direction to cancel the antenna current transmitting in circuit board  108 , so that it is possible to actively use the ground part of circuit board  105  as an antenna. 
         [0071]    Therefore, besides the above effect of embodiment 1, the present embodiment uses the ground part of the circuit board, which is provided in the first casing located above the second casing, in an open state, as an antenna, so that it is possible to radiate a wave from the circuit board provided in the first casing. By this means, it is possible to expand the distance from the hand holding the second casing to the circuit board radiating a wave, and therefore to achieve good antenna performance. The present embodiment can use a cable used to transmit a signal from the circuit board provided in the second casing to the circuit board provided in the first casing, as a cable to transmit the antenna current on the circuit board provided in the first casing. By this means, there is no need to newly provide a special cable to transmit antenna current on the circuit board provided in the first casing, so that it is possible to gain good antenna performance without increasing the manufacturing cost. 
         [0072]    Although with the present embodiment a reactance element is not provided in slit  110 , the present embodiment is not limited to this, and, as shown in  FIG. 4 , it is possible to provide a reactance element between end parts forming slit  110  in a circuit board. Although with the present embodiment a slit is formed from one end part of the circuit board, the present embodiment is not limited to this, and it is equally possible to form a slit that extends from any arbitrary location in the circuit board. 
       Embodiment 4 
       [0073]      FIG. 6  is a side view of portable radio device  600  according to the embodiment 4 of the present invention in an open state. 
         [0074]    Compared to potable radio device  100  according to embodiment 1 shown in  FIG. 1 , portable radio device  600  shown in  FIG. 6  removes antenna  107  and adds power feeding line  601 . Also, parts in  FIG. 6  that are the same as in  FIG. 1  will be assigned the same reference numerals as in  FIG. 1  and overlapping descriptions will be omitted. 
         [0075]    Portable radio device  600  is mainly formed with first casing  101 , second casing  102 , first slide mechanism section  103 , second slide mechanism section  104 , circuit board  105 , display section  106 , circuit board  108 , power feeding section  109 , and power feeding line  601 . 
         [0076]    Power feeding section  109  is provided above circuit board  108 . Power feeding section  109  feeds power to the ground part of circuit board  105  through power feeding line  601 . 
         [0077]    Power feeding line  601  electrically connects power feeding section  109  and circuit board  105 , and feeds power to the ground part of circuit board  105 . In this case, power feeding line  601  feeds power to the ground part of circuit board  105  above slit  110 . 
         [0078]    Circuit board  105  is provided in first casing  101  and display section  106  such as LCD is attached. Circuit board  105  has slit  110  extending from one end in a perpendicular direction to a slide direction (a vertical direction in  FIG. 6 ) of first casing  101  and penetrates circuit board  105  in a thickness direction. When first casing  101  and second casing  102  are in an open state, slit  110  is located lower (lower than broken line P 1  in  FIG. 6 ) than power feeding section  109 . Above slit  110 , the ground part of circuit board  105  is fed power from power feeding section  109  through power feeding line  601 . A “slit” is not mandatory and, as the embodiment 1, as long as an insulation section is provided, it is possible to achieve the effect of the present embodiment. 
         [0079]    Next, the flow of antenna current in portable radio device  600  will be described. 
         [0080]    In the ground part of circuit board  108  in portable radio device  600 , antenna current e 3  transmits towards power feeding section  109 , that is, upward in  FIG. 6  The ground part of circuit board  105  is fed power from power feeding section  109  through power feeding line  601 , so that antenna current e 4  transmits from the connecting part of circuit board  105  and power feeding line  601  upward in  FIG. 6 . Thus, antenna current e 4  transmitting in circuit board  105  transmits in the same direction as antenna current e 3  transmitting in circuit board  108 . On the other hand, the ground part of circuit board  105  provides slit  110  and therefore suppresses the current transmitting downward in  FIG. 6 . By this means, circuit board  105 , circuit board  108 , and power feeding section  109  can form a dipole antenna. 
         [0081]    In fact, conventionally, in circuit board  105 , current transmits in the direction to cancel antenna current e 3  of circuit board  108 , so that, if power feeding section  109  feeds power to the ground part of circuit board  105 , the current transmitting in the direction to cancel antenna current e 3  is increased. Thus, conventionally, it has been impossible to form a dipole antenna. On the other hand, circuit board  105  of the present embodiment suppresses the current transmitting in the direction to cancel the antenna current transmitting in circuit board  108 , so that it is possible to actively use the ground part of circuit board  105  as an antenna and to form a dipole antenna. 
         [0082]    Besides the above effect of embodiment 1, by feeding power to the ground part of the circuit board provided in the first casing, the present embodiment can form a dipole antenna. 
         [0083]    Although with the present embodiment a reactance element is not formed in slit  110 , the present embodiment is not limited to this, and as shown in  FIG. 4  it is possible to provide a reactance element between end parts forming slit  110  in a circuit board. Although with the present embodiment a slit is formed from one end part of a circuit board, the present embodiment is not limited to this, and it is equally possible to form a slit that extends from any arbitrary location in the circuit board. 
       Embodiment 5 
       [0084]      FIG. 7  is a plan view of first casing  750  according to embodiment 5 of the present invention. 
         [0085]    Compared to first casing  101  according to embodiment 1 shown in  FIG. 3 , first casing  750  shown in  FIG. 7  has circuit board  700  instead of circuit board  105 . Compared to circuit board  105  according to embodiment 1 shown in  FIG. 3 , circuit board  750  shown in  FIG. 7  has slit  701  and slit  702  instead of slit  110  and has narrow section  703  instead of narrow section  304 . Also, parts in  FIG. 7  that are the same as in  FIG. 3  will be assigned the same reference numerals as in  FIG. 3  and overlapping descriptions will be omitted. The portable radio device except first casing  750  according to the present embodiment is the same as the above embodiment land the descriptions will be omitted. 
         [0086]    First casing  750  is formed in a rectangular shape in a plan view and is slidably attached to second casing  102  to switch from an open state to a closed state or to switch from a closed state to an open state, by sliding with first slide mechanism section  103 . Thus, first casing  750  is attached to second casing  102  to be able to slide in the lengthwise direction of first casing  750 . In an open state, first casing  750  slides with first slide member  103  that is bent to erect, and therefore is held on second casing  102  in an erect state. First casing  750  has circuit board  700  and display section  106 . 
         [0087]    Circuit board  700  is provided in first casing  750  and display section  106  such as LCD is attached. Circuit board  700  has slit  701  and slit  702  extend from an end part in a perpendicular direction to a slide direction of first casing  750  and penetrate circuit board  700  in a thickness direction. When first casing  750  and second casing  102  are in an open state, slit  701  and slit  702  are located lower than antenna  107  and power feeding section  109 . Here, slit  701  and slit  702  are provided to suppress the current to travel in the lower part than slit  701  and slit  702  in circuit board  700 . Thus, a “slit” is not mandatory, and, as long as an insulation section is provided, it is possible to achieve the effect of the present embodiment. In the present embodiment, a case will be described where slit  701  and slit  702  are provided as one example of an insulation section. 
         [0088]    Specifically, on a plan view, circuit board  700  is provided almost over the entire surface of first casing  750 . In circuit board  700 , slit  701  is formed from one end part  301 , which is in the lateral direction (a horizontal direction in  FIG. 7 ) of circuit board  700 , in a perpendicular direction to a slide direction (a vertical direction in  FIG. 7 ) of first casing  101 . In circuit board  700 , slit  702  is formed from one end part  302 , which opposes to end part  301  in the lateral direction of circuit board  700 , in a perpendicular direction to a slide direction of first casing  750 . By providing slit  701  and slit  702 , circuit board  700  forms narrow section  703 . Circuit board  700  defines slit  701  and slit  702  as a boundary, provides display section  106  in the upper part (the upper part in  FIG. 7 ), and provides operation key section  303  in the lower part (the lower part in  FIG. 3 ). In narrow section  703  of circuit board  700 , circuit patterns (not shown) are formed to transmit the signals input from operation key section  303 , to a signal processing section such as a CPU (not shown) mounted on circuit board  700 . 
         [0089]    Slit  701  is a through hole that is formed in circuit board  700  and that penetrates circuit board  700  in a thickness direction (a perpendicular direction to the sheet of  FIG. 7 ). It is possible to change the total length (see  FIG. 7 ) of width r 10  from end part  301  of slit  701  and width r 11  from end part  302  of slit  702 , according to the frequency used by the portable radio device. 
         [0090]    As conventionally known, the portable radio device having the above configuration electrically connects circuit board  750  and circuit board  108 , in an open state, at the point where circuit board  700  and circuit board  108  overlap one above the other. However, the present embodiment provides slit  701  and slit  702  to electrically disconnect area r 2  in circuit board  700  below slit  701  and slit  702 , and therefore suppresses the current transmitting in area r 2  in circuit board  700  below slit  701  and slit  702 . Thus, although conventionally in area r 2 , the current has transmitted in a direction to cancel the antenna current transmitting upward on circuit board  108  towards power feeding section  109  of antenna  107 , the present embodiment provides slit  701  and slit  702  to suppress the current transmitting in area r 2 . By this means, the present embodiment can prevent antenna performance degradation of antenna  107 . 
         [0091]    Therefore, the present embodiment provides, in a circuit board provided in the first casing, a slit that is located lower than a power feeding section in an open state, so that it is possible to electrically disconnect the part of the circuit board below the slit, and to prevent antenna performance degradation when a slide mechanism using a metal member is provided. The present embodiment provides an operation key section having a simple configuration below the slit provided in the circuit board, so that it is possible to provide the circuit patterns in a narrow area that is created by providing the slit. With the circuit board provided in the first casing, the present embodiment suppresses the current transmitting in the area below the slit and also provides an operation key section in the area below the slit, so that it is possible to reduce the influence to the antenna current caused by a hand operating the operation key section. 
         [0092]    The present embodiment may provide a reactance element in slit  701  and slit  702 .  FIG. 8  is a plan view of first casing  750  showing another example of the circuit board according to the present embodiment. From  FIG. 8 , the present embodiment may provide reactance element  801  to electrically connect between end parts forming slit  701  of circuit board  700 .  FIG. 9  is a plan view of first casing  750  showing yet another example of the circuit board according to the present embodiment. From  FIG. 9 , the present embodiment may provide reactance element  901  to electrically connect between end parts forming slit  702  of circuit board  700 .  FIG. 10  is a plan view of first casing  750  showing yet another example of the circuit board according to the present embodiment. From  FIG. 10 , the present embodiment may provide reactance element  1001  to electrically connect between end parts forming slit  701  of circuit board  700  and reactance element  1002  to electrically connect between end parts forming slit  702  of circuit board  700 . 
         [0093]    Although the present embodiment extends and forms the slit from an end part of the circuit board, the present embodiment is not limited to this, and it is possible to extend and form the slit from an arbitrary location of the circuit board. 
       Embodiment 6 
       [0094]      FIG. 11  is a plan view of first casing  1150  according to embodiment 6 of the present invention. 
         [0095]    Compared to first casing  101  according to embodiment 1 shown in  FIG. 3 , first casing  1150  shown in  FIG. 11  adds connection line  1102  and has circuit board  1100  and circuit board  1101  instead of circuit board  105 . Also, parts in  FIG. 11  that are the same as in  FIG. 3  will be assigned the same reference numerals as in  FIG. 3  and overlapping descriptions will be omitted. The portable radio device except first casing  1150  according to the present embodiment is the same as the above embodiment 1 and the descriptions will be omitted. 
         [0096]    First casing  1150  is formed in a rectangular shape in a plan view and is slidably attached to second casing  102  by sliding with first slide mechanism section  103 , to switch from an open state to a closed state or to switch from a closed state to an open state. Thus, first casing  1150  is attached to second casing  102  to be able to slide in the lengthwise direction of first casing  1150 . In an open state, first casing  1150  slides with first slide member  103  that is bent to erect, and is held on second casing  102  in an erect state. First casing  1150  has circuit board  1100 , circuit board  1101 , connection line  1102 , and display section  106 . 
         [0097]    Circuit board  1100  is provided in first casing  1150  and display section  106  such as LCD is attached. Circuit board  1100  is electrically connected with circuit board  1101  by connection line  1102 . 
         [0098]    Circuit board  1101  is provided in first casing  1150  and, in an open state, is located lower than antenna  107  and power feeding section  109 . 
         [0099]    Connection line  1102  is, for example, a flexible cable (FPC) and electrically connects end part of circuit board  1100  and end part of circuit board  1101 . Connection line  1102  transmits the signals input from operation key section  303  to a signal processing section such as a CPU (not shown) mounted on circuit board  1100 . 
         [0100]    Circuit board  1100 , circuit board  1101 , and connection line  1102  form slit  110 . 
         [0101]    In an open state, the portable radio device having the above configuration, electrically connects circuit board  1101  and circuit board  108  through first slide mechanism section  103  and second slide mechanism section  104 . However, the present embodiment provides slit  110  to electrically disconnect circuit board  1101  below slit  110 , and therefore suppresses the current transmitting in circuit board  1101 . Thus, although conventionally in area r 2 , the current has transmitted in a direction to cancel the antenna current transmitting upward on circuit board  108  towards power feeding section  109  of antenna  107 , the present embodiment provides slit  110  to suppress the current transmitting in circuit board  1101 . By this means, the present embodiment can prevent antenna performance degradation of antenna  107 . 
         [0102]    Therefore, the present embodiment provides, in a circuit board provided in the first casing, a slit that is located lower than a power feeding section in an open state, so that it is possible to electrically disconnect the part of the circuit board below the slit, and to prevent antenna performance degradation when a slide mechanism using a metal member is provided. The present embodiment provides an operation key section having a simple configuration below the slit provided in the circuit board, so that it is possible to provide the circuit patterns in a narrow area that is created by providing the slit. With the circuit board provided in the first casing, the present embodiment suppresses the current transmitting in the area below the slit and also provides an operation key section in the area below the slit, so that it is possible to reduce the influence to the antenna current caused by a hand operating the operation key section. 
         [0103]    The present embodiment may provide a reactance element in slit  110 .  FIG. 12  is a plan view of first casing  1150  showing another example of the circuit board according to the present embodiment. From  FIG. 12 , the present embodiment may provide reactance element  1201  to electrically connect between end part of circuit board  1100  and end part of circuit board  1101  forming slit  110 . 
       Embodiment 7 
       [0104]      FIG. 13  is a plan view of first casing  1350  according to embodiment 7 of the present invention. 
         [0105]    Compared to first casing  101  according to embodiment 1 shown in  FIG. 3 , first casing  1350  shown in  FIG. 13  adds metal section  1301  and has circuit board  1300  instead of circuit board  105 . Also, parts in  FIG. 13  that are the same as in  FIG. 3  will be assigned the same reference numerals as in  FIG. 3  and overlapping descriptions will be omitted. The portable radio device except first casing  1350  according to the present embodiment is the same as the above embodiment 1 and the descriptions will be omitted. 
         [0106]    First casing  1350  is formed in a rectangular shape in a plan view and is slidably attached to second casing  102  to switch from an open state to a closed state or to switch from a closed state to an open state, by sliding with first slide mechanism section  103 . Thus, first casing  1350  is attached to second casing  102  to be able to slide along the lengthwise direction of first casing  1350 . In an open state, by sliding with first slide member  103  that is bent to erect, first casing  1350  is held on second casing  102  in an erect state. First casing  1350  has circuit board  1300 , metal section  1301 , and display section  106 . 
         [0107]    Circuit board  1300  is provided in the upper part of first casing  1350  and display section  106  such as LCD is attached. Also, circuit board  1300  is electrically connected with metal section  1301 . 
         [0108]    Metal section  1301  is flat and is provided in the lower part of first casing  1350 . In metal section  1301 , projecting strip section  1303  is formed to be electrically connected with circuit board  1300  at connecting part  1302 , and therefore is electrically connected with circuit board  1300 . Metal section  1301  functions as the ground part of antenna  107 . 
         [0109]    Circuit board  1300  and metal sections  1301  form slit  110 . The length of width r 1  (see  FIG. 13 ) from end part  1310  of circuit board  1300  of slit  110  makes, for example, the perimeter of metal section  1301  as half-wavelength (λ/2) of the frequency used by the portable radio device. The higher the frequency used by the portable radio device, the smaller the perimeter in metal section  1301  is placed. Here, the perimeter of metal section  1301  is referred to the length ( 15  in  FIG. 13 ) along slit  110  and end parts  1311 ,  1312 , and  1313  of metal section  1301 . 
         [0110]    In an open state, the portable radio device having the above configuration, electrically connects metal section  1301  and circuit board  108  through first slide mechanism section  103  and second slide mechanism section  104 . However, the present embodiment provides slit  110  to electrically disconnect metal section  1301  below slit  110 , and therefore suppresses the current transmitting in metal section  1301 . By this means, in the present embodiment, it is possible to prevent degradation of antenna performance of antenna  107 . 
         [0111]    Therefore, the present embodiment provides, in a circuit board provided in the first casing, a slit that is located lower than a power feeding section in an open state, so that it is possible to electrically disconnect the part of the circuit board below the slit, and to prevent antenna performance degradation when a slide mechanism using a metal member is provided. The present embodiment provides an operation key section having a simple configuration below the slit provided in the circuit board, so that it is possible to provide the circuit patterns in a narrow area that is created by providing the slit. With the circuit board provided in the first casing, the present embodiment suppresses the current transmitting in the area below the slit and also provides an operation key section in the area below the slit, so that it is possible to reduce the influence to the antenna current caused by a hand operating the operation key section. 
         [0112]    The present embodiment may provide a reactance element in slit  110 .  FIG. 14  is a plan view of the first casing showing another example of the first casing according to the present embodiment. From  FIG. 14 , the present embodiment may provide reactance element  1401  to electrically connect between end part of circuit board  1300  and end part of metal section  1301  forming slit  110 . 
       Embodiment 8 
       [0113]      FIG. 15  is a plan view of first casing  1550  according to embodiment 8 of the present invention. 
         [0114]    Compared to first casing  101  according to embodiment 1 shown in  FIG. 3 , first casing  1550  shown in  FIG. 15  adds metal section  1501  and metal section  1502  and has circuit board  1500  instead of circuit board  105 . Also, parts in  FIG. 15  that are the same as in  FIG. 3  will be assigned the same reference numerals as in  FIG. 3  and overlapping descriptions will be omitted. The portable radio device except first casing  1550  according to the present embodiment is the same as the above embodiment 1 and the descriptions will be omitted. 
         [0115]    First casing  1550  is formed in a rectangular shape in a plan view and is slidably attached to second casing  102  to switch from an open state to a closed state or to switch from a closed state to an open state, by sliding with first slide mechanism section  103 . Thus, first casing  1550  is attached to second casing  102  to be able to slide along the lengthwise direction of first casing  1550 . In an open state, by sliding with first slide mechanism section  103  that is bent to erect, first casing  1550  is held on second casing  102  in an erect state. First casing  1550  has circuit board  1500 , metal section  1501 , metal section  1502 , and display section  106 . 
         [0116]    Circuit board  1500  is provided in the upper part of first casing  1550  and display section  106  such as LCD is attached. Circuit board  1500  is electrically connected with circuit board  1502  at connecting part  1503 . 
         [0117]    Metal section  1501  is flat and is provided in the lower part of first casing  1550 . At connecting part  1504 , metal section  1501  is electrically connected with circuit board  1502 . Metal section  1501  functions as the ground part of antenna  107 . 
         [0118]    Metal section  1502  is flat, electrically connects with circuit board  1500  at connecting part  1503 , and also electrically connects with metal section  1501  at connecting part  1504 . Thus, metal section  1502  electrically connects circuit board  1500  and metal section  1501 . 
         [0119]    Circuit board  1500 , metal section  1501 , and metal section  1502  form slit  110 . The length of width r 1  (see  FIG. 15 ) from end part  1510  of circuit board  1500  of slit  110  makes, for example, the perimeter of metal section  1501  as half-wavelength (λ/2) of the frequency used by the portable radio device. The higher the frequency used by the portable radio device, the smaller the perimeter of metal section  1501  is placed. Here, the perimeter of metal section  1501  is referred to the length ( 17  in  FIG. 15 ) along slit  110  and end parts  1511 ,  1512 , and  1513  of metal section  1501 . 
         [0120]    In an open state, the portable radio device having the above configuration, electrically connects metal section  1501  and circuit board  108  through first slide mechanism section  103  and second slide mechanism section  104 . However, the present embodiment provides slit  110  to electrically disconnect metal section  1501  below slit  110 , and therefore suppresses the current transmitting in metal section  1501 . By this means, the present embodiment prevents antenna performance degradation of antenna  107 . 
         [0121]    Therefore, the present embodiment provides, in a circuit board provided in the first casing, a slit that is located lower than a power feeding section in an open state, so that it is possible to electrically disconnect the part of the circuit board below the slit, and to prevent antenna performance degradation when a slide mechanism using a metal member is provided. The present embodiment provides an operation key section having a simple configuration below the slit provided in the circuit board, so that it is possible to provide the circuit patterns in a narrow area that is created by providing the slit. With the circuit board provided in the first casing, the present embodiment suppresses the current transmitting in the area below the slit and also provides an operation key section in the area below the slit, so that it is possible to reduce the influence to the antenna current caused by a hand operating the operation key section. 
         [0122]    The present embodiment may provide a reactance element in slit  110 .  FIG. 16  is a plan view of the first casing showing another example of the first casing according to the present embodiment. From  FIG. 16 , the present embodiment may provide reactance element  1601  to electrically connect between end part of circuit board  1500  and end part of metal section  1501  forming slit  110 . 
       Embodiment 9 
       [0123]      FIG. 17  is a side view of portable radio device  1700  according to the embodiment 9 of the present invention in an open state. 
         [0124]    Compared to portable radio device  100  according to embodiment 1 shown in  FIG. 1 , portable radio device  1700  shown in  FIG. 17  has first casing  1750  instead of first casing  101 . Compared to first casing  101  of portable radio device  100  according to embodiment 1 shown in  FIG. 1 , first casing  1750  of portable radio device  1700  shown in  FIG. 17  adds metal section  1702  and has circuit board  1701  instead of circuit board  105 . Also, parts in  FIG. 17  that are the same as in  FIG. 1  will be assigned the same reference numerals as in  FIG. 1  and overlapping descriptions will be omitted. 
         [0125]    Portable radio device  1700  is mainly formed by second casing  102 , first slide mechanism section  103 , second slide mechanism section  104 , display section  106 , antenna  107 , circuit board  108 , power feeding section  109 , circuit board  1701 , metal section  1702  and first casing  1750 . 
         [0126]    First casing  1750  is formed in a rectangular shape in a plan view and is slidably attached to second casing  102  to switch from the open state of  FIG. 17  to a closed state or to switch from a closed state to the open state of  FIG. 17 , by sliding with first slide mechanism section  103 . Thus, first casing  1750  is attached to second casing  102  to be able to slide along the lengthwise direction (a vertical direction in  FIG. 17 ) of first casing  1750 . In the open state of  FIG. 17 , by sliding with first slide mechanism section  103  that is bent to erect, first casing  1750  is held on second casing  102  in an erect state. First casing  1750  has display section  106 , circuit board  1701 , and metal section  1702 . 
         [0127]    Second casing  102  is formed in a rectangular shape in a plan view and is slidably attached to first casing  1750  to switch from the open state of  FIG. 17  to a closed state or to switch from a closed state to the open state of  FIG. 17 , by sliding with second slide mechanism section  104 . Also, second casing  102  has second slide mechanism section  104  and circuit board  108 . Second casing  102  has antenna  107  on the upper end part (the upper end part of  FIG. 17 ). In an open state, second casing  102  holds first casing  1750  in an erect state as shown in  FIG. 17 , and overlaps with first casing  1750  in a closed state. 
         [0128]    First slide mechanism section  103  is formed by bending a metal plate. Also, first slide mechanism section  103  slides in a vertical direction in  FIG. 17 , guided by a rail (not shown) provided in second slide mechanism section  104 . First slide mechanism section  103  is attached to first casing  1750  and slides with first casing  1750 . By sliding along a bent and erect shape guided by second slide mechanism section  104 , in an open state, first slide mechanism section  103  holds first casing  1750  in an erect state with respect to second casing  102 . 
         [0129]    Circuit board  1701  is provided in first casing  1750  and display section  106  such as LCD is attached. 
         [0130]    Display section  106  is, for example, a liquid crystal display apparatus (LCD) and is attached to circuit board  1701 . Display section  106  shows, for example, image data that portable radio device  1700  receives. 
         [0131]    Circuit board  108  is provided in second casing  102 , and antenna  107  and power feeding section  109  are provided in its upper end part. In the open state of  FIG. 17 , on a plan view, the upper side of circuit board  108  overlaps with the lower side of circuit board  1701  and metal section  1702  (part between broken line P 11  and broken line P 12  in  FIG. 17 ). 
         [0132]    Metal section  1702  is flat, and is provided in a back face side of circuit board  1701  of first casing  1750 . Metal section  1702  has slit  1703  extending from one end in a perpendicular direction to a slide direction of first casing  1750  and penetrates metal section  1702  in a thickness direction (a horizontal direction in  FIG. 17 ). When first casing  1750  and second casing  102  are placed in an open state, slit  1703  is located lower (lower than broken line P 11  in  FIG. 17 ) than antenna  107  and power feeding section  109 . Metal section  1702  functions as the ground part of antenna  107 . Now, the details of slit  1703  will be described later. 
         [0133]    Next, a detailed configuration of metal section  1702  will be described using  FIG. 18 .  FIG. 18  is a plan view of metal section  1702 . 
         [0134]    In metal section  1702 , slit  1703  is formed from one end part  1801  of metal section  1702  in a perpendicular direction to a slide direction (a vertical direction in  FIG. 18 ) of first casing  1750 . 
         [0135]    Slit  1703  is a through hole that is formed in metal section  1702  and that penetrates metal section  1702  in a thickness direction (a perpendicular direction to the sheet of  FIG. 18 ). The length of width r 21  (see  FIG. 18 ) from end part  1801  of slit  1703  makes, for example, the perimeter of the lower side of slit  1703  in metal section  1702  as half-wavelength (λ/2) of the frequency used by portable radio device  1700 . The higher the frequency used by portable radio device  1700 , the smaller the perimeter below slit  1703  in metal section  1702  is placed. Here, in area r 22  below slit  1703  in metal section  1702 , the perimeter below slit  1703  in metal section  1702  is referred to the length ( 110  in  FIG. 18 ) along slit  1703  and end parts  1801 ,  1802 , and  1803  of metal section  1702 . 
         [0136]    Next, the reason antenna performance of antenna  107  is not degraded in portable radio device  1700  having the above configuration will be explained. 
         [0137]    In the open state of  FIG. 17 , metal section  1702  and circuit board  108  are electrically connected at the part (part between P 11  and P 12 ) where metal section  1702  and circuit board  108  overlap one above the other, through first slide mechanism section  103  and second slide mechanism section  104 . However, the present embodiment provides slit  1703  to electrically disconnect area r 22  below slit  1703  in metal section  1702 , and therefore suppresses the current transmitting in area r 22  below slit  1703  in metal section  1702 . Thus, the current transmitting in a direction to cancel the antenna current transmitting upward in  FIG. 17  on circuit board  108  towards power feeding section  109 , is suppressed. By this means, the present embodiment can prevent antenna performance degradation of antenna  107 . 
         [0138]    Therefore, the present embodiment provides, in a circuit board provided in the first casing, a slit that is located lower than a power feeding section in an open state, so that it is possible to electrically disconnect the part of the circuit board below the slit, and to prevent antenna performance degradation when a slide mechanism using a metal member is provided. The present embodiment provides an operation key section having a simple configuration below the slit provided in the circuit board, so that it is possible to provide the circuit patterns in a narrow area that is created by providing the slit. With the circuit board provided in the first casing, the present embodiment suppresses the current transmitting in the area below the slit and also provides an operation key section in the area below the slit, so that it is possible to reduce the influence to the antenna current caused by a hand operating the operation key section. 
         [0139]    The present embodiment may provide a reactance element in slit  110 .  FIG. 19  is a plan view of a metal section showing another example of the metal section of the present embodiment. From  FIG. 19 , the present embodiment may provide reactance element  1901  to electrically connect between end parts forming slit  1703  of metal section  1702 . Although the present embodiment forms slit  1703  in one metal section  1702 , the present invention is not limited to this, and it is equally possible to connect multiple metal sections to form the slit.  FIG. 20  is a plan view of a metal section showing yet another example of a metal section of the present embodiment. From  FIG. 20 , metal sections  2001 ,  2002 , and  2003  may form slit  2006 . Thus, metal section  2001  is flat, electrically connects with metal section  2003  in connecting part  2004 , and metal section  2002  electrically connects with metal section  2003  in connecting part  2005 . 
         [0140]    The above embodiments 1-5 can achieve the effect of the present invention without forming the slit on the circuit board, as described in each embodiment.  FIG. 21  is a plan view of first casing  101  showing another example of the circuit board according to the above embodiments 1-4. Thus, from  FIG. 21 , circuit board  2100  may provide insulation section  2101 , where metal pattern  2102  is not formed, instead of slit  110 . This configuration can electrically disconnect the lower part of insulation section  2101  in circuit board  2100 , so that it is possible to prevent antenna performance degradation. The same applies to the above embodiment 5, so that the description will be omitted. 
         [0141]    Although the above embodiments 1-9 are designed to switch from a closed state to an open state when the first casing slides to erect from a second casing, the present invention is not limited to this, and the first casing may slide parallel to a second casing from a closed state to be an open state, and the slide structure may adopt an arbitrary method. 
         [0142]    Although the above embodiments 1-9 form a slit that extends in a perpendicular direction to the slide direction of the first casing, the present invention is not limited to this, and it is equally possible to form a slit to extend in any arbitrary direction as long as it crosses the slide direction of the first casing. 
         [0143]    In the above embodiments 1-9, the shape of the slit does not necessarily have to be a linear shape but can be an arbitrary shape according to the frequency used by the portable radio device.  FIG. 22  is a plan view of the first casing  101  showing another example of the slit provided in circuit board  105  according to embodiments 1-4. As  FIG. 22  shows, by providing a concave and convex in the bottom part of slit  2201 , it is possible to change the perimeter below the slit in a circuit board according to the used frequency. Also, it is equally possible to adjust the perimeter below the slit in a circuit board, by adjusting the depth length of the slit (the length of r 1  in  FIG. 3 ) or by adjusting the depth length of the slit and the concave-convex shape provided in the bottom part of the slit. Generally, the lower the used frequency is, the longer the perimeter below the slit in a circuit board is. The same applies to the above embodiments 5-9, so that the descriptions will be omitted. 
         [0144]    Although the above embodiments 1-6 provide an operation key section in the lower side than the slit of a circuit board, the present invention is not limited to this, and it is equally possible to provide any arbitrary member other than an operation key section may be arranged. 
         [0145]    The disclosure of Japanese Patent Application No. 2009-3635, filed on Jan. 9, 2009, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0146]    A portable radio device of the present invention is especially suitable to connect a plurality of casings in a mutually slidable fashion and is placed in an open state and a closed state in accordance with slide operations.