An image detector for bank notes comprising a pair of detector units, each of said pair of detector units comprising: an image detection sensor for detecting an image of a first detection area (Z1, Z1') set on one side of said detector unit, and a first light emitting device for irradiating light towards the first detection area (Z1, Z1'), characterized in that: each of said pair of detector units further comprises a second light emitting device for irradiating light towards a second detection area (Z2, Z2') set on the one side of said detector unit, the second detection area (Z2, Z2') being located in a different location from the first detection area (Z1, Z1'), said image detection sensor, said first light emitting device and said second light emitting device are disposed in each of said pair of detector units, said pair of detector units are disposed so as to oppose one another across a bank note transportation path, in a manner which enables said image detection sensor in one of said pair of detection units to detect an image of the second detection area of the other of said pair of detection units and enables said image detection sensor in the other of said pair of detection units to detect an image of the second detection area of the one of said pair of said detection units, and a distance from one end of a unit main body of said detector unit to the first detection area (Z1, Z1') is equal to a distance from the other end of the unit main body of said detector unit to the second detection area (Z2, Z2'). an image detection sensor for detecting an image of a first detection area (Z1, Z1') set on one side of said detector unit, and a first light emitting device for irradiating light towards the first detection area (Z1, Z1'), characterized in that: each of said pair of detector units further comprises a second light emitting device for irradiating light towards a second detection area (Z2, Z2') set on the one side of said detector unit, the second detection area (Z2, Z2') being located in a different location from the first detection area (Z1, Z1'), said image detection sensor, said first light emitting device and said second light emitting device are disposed in each of said pair of detector units, said pair of detector units are disposed so as to oppose one another across a bank note transportation path, in a manner which enables said image detection sensor in one of said pair of detection units to detect an image of the second detection area of the other of said pair of detection units and enables said image detection sensor in the other of said pair of detection units to detect an image of the second detection area of the one of said pair of said detection units, and a distance from one end of a unit main body of said detector unit to the first detection area (Z1, Z1') is equal to a distance from the other end of the unit main body of said detector unit to the second detection area (Z2, Z2'). each of said pair of detector units further comprises a second light emitting device for irradiating light towards a second detection area (Z2, Z2') set on the one side of said detector unit, the second detection area (Z2, Z2') being located in a different location from the first detection area (Z1, Z1'), said image detection sensor, said first light emitting device and said second light emitting device are disposed in each of said pair of detector units, said pair of detector units are disposed so as to oppose one another across a bank note transportation path, in a manner which enables said image detection sensor in one of said pair of detection units to detect an image of the second detection area of the other of said pair of detection units and enables said image detection sensor in the other of said pair of detection units to detect an image of the second detection area of the one of said pair of said detection units, and a distance from one end of a unit main body of said detector unit to the first detection area (Z1, Z1') is equal to a distance from the other end of the unit main body of said detector unit to the second detection area (Z2, Z2').