An automatic analysis apparatus, comprising: a housing; a vessel disposed at a predetermined position in the housing; an opening for taking the vessel into/from the housing, which is provided in the housing; an operating unit which is operated to take the vessel into/from the housing via the opening; a transport mechanism which transports the vessel from the predetermined position to a vessel takeout position along with the operation of the operating unit; and a speed change mechanism which reduces an operation amount of the operating unit as compared with a movement amount of the vessel from the predetermined position to the vessel takeout position, wherein a movement direction of the operating unit and a movement direction of the vessel are the same when the vessel is taken in/out, the transport mechanism includes: a first rail which slidably supports the housing and the operating unit and extends in the movement direction of the operating unit; a second rail which slidably supports the operating unit and the vessel and extends in the movement direction of the vessel, a belt which bridges across a pair of pulleys (49, 50) provided in the operating unit to be looped thereover; transmission means for transmitting the operation of the operating unit to a rotation of the pulleys (49, 50); and a connecting member which moves the vessel along with traveling of the belt, characterised in that the pair of pulleys (49, 50) are provided with vertical rotational shafts (47, 48), a pair of the first rails provided on outer sides of the belt facing across the rotational shafts (47, 48), and a pair of the second rails provided on outer sides of the first rails facing across the first rails, and the first rails, the second rails, and the belt bolto are placed side by side without overlapping with each other in a vertical direction. a housing; a vessel disposed at a predetermined position in the housing; an opening for taking the vessel into/from the housing, which is provided in the housing; an operating unit which is operated to take the vessel into/from the housing via the opening; a transport mechanism which transports the vessel from the predetermined position to a vessel takeout position along with the operation of the operating unit; and a speed change mechanism which reduces an operation amount of the operating unit as compared with a movement amount of the vessel from the predetermined position to the vessel takeout position, wherein a movement direction of the operating unit and a movement direction of the vessel are the same when the vessel is taken in/out, the transport mechanism includes: a first rail which slidably supports the housing and the operating unit and extends in the movement direction of the operating unit; a second rail which slidably supports the operating unit and the vessel and extends in the movement direction of the vessel, a belt which bridges across a pair of pulleys (49, 50) provided in the operating unit to be looped thereover; transmission means for transmitting the operation of the operating unit to a rotation of the pulleys (49, 50); and a connecting member which moves the vessel along with traveling of the belt, characterised in that the pair of pulleys (49, 50) are provided with vertical rotational shafts (47, 48), a pair of the first rails provided on outer sides of the belt facing across the rotational shafts (47, 48), and a pair of the second rails provided on outer sides of the first rails facing across the first rails, and the first rails, the second rails, and the belt bolto are placed side by side without overlapping with each other in a vertical direction. a first rail which slidably supports the housing and the operating unit and extends in the movement direction of the operating unit; a second rail which slidably supports the operating unit and the vessel and extends in the movement direction of the vessel, a belt which bridges across a pair of pulleys (49, 50) provided in the operating unit to be looped thereover; transmission means for transmitting the operation of the operating unit to a rotation of the pulleys (49, 50); and a connecting member which moves the vessel along with traveling of the belt, characterised in that the pair of pulleys (49, 50) are provided with vertical rotational shafts (47, 48), a pair of the first rails provided on outer sides of the belt facing across the rotational shafts (47, 48), and a pair of the second rails provided on outer sides of the first rails facing across the first rails, and the first rails, the second rails, and the belt bolto are placed side by side without overlapping with each other in a vertical direction.