An automatic analysis device, comprising: a heat block which includes a plurality of positions on which reaction containers in which reaction liquid mixing a reagent and a sample is injected are mounted; and a strip-shaped heater which heats the heat block, wherein the strip-shaped heater is wound and attached on an outer circumference of the heat block so that both end regions of the strip-shaped heater are adjacent to each other, wherein the strip-shaped heater includes a heat generating resistor made from stainless steel foil or nichrome foil having a uniform thickness in the longitudinal direction which generates heat by applying an electric current, an insulating film which electrically insulates with respect to an outside portion by disposing to sandwich the heat generating resistor, and a first and a second electricity feeding lines (8, 8a) which are attached to both end portions of the heat generating resistor and supply power to the heat generating resistor, and wherein the width of the heat generating resistor in both end regions of the strip-shaped heater is formed in a way that a first electrode portion and a second electrode portion are wider than the other regions of the heat generating resistor, wherein the vicinities of the first electrode portion and the second electrode portion are narrow portions which are narrower than the other regions of the heat generating resistor, characterized in that the heat generating resistor is disposed so that both end regions of the strip-shaped heater face each other with a predetermined interval being sandwiched therebetween by both ends in the longitudinal direction of the strip-shaped heater, the strip-shaped heater being folded in the longitudinal end regions, wherein the narrow portions are adjacent to each other. a heat block which includes a plurality of positions on which reaction containers in which reaction liquid mixing a reagent and a sample is injected are mounted; and a strip-shaped heater which heats the heat block, wherein the strip-shaped heater is wound and attached on an outer circumference of the heat block so that both end regions of the strip-shaped heater are adjacent to each other, wherein the strip-shaped heater includes a heat generating resistor made from stainless steel foil or nichrome foil having a uniform thickness in the longitudinal direction which generates heat by applying an electric current, an insulating film which electrically insulates with respect to an outside portion by disposing to sandwich the heat generating resistor, and a first and a second electricity feeding lines (8, 8a) which are attached to both end portions of the heat generating resistor and supply power to the heat generating resistor, and wherein the width of the heat generating resistor in both end regions of the strip-shaped heater is formed in a way that a first electrode portion and a second electrode portion are wider than the other regions of the heat generating resistor, wherein the vicinities of the first electrode portion and the second electrode portion are narrow portions which are narrower than the other regions of the heat generating resistor, characterized in that the heat generating resistor is disposed so that both end regions of the strip-shaped heater face each other with a predetermined interval being sandwiched therebetween by both ends in the longitudinal direction of the strip-shaped heater, the strip-shaped heater being folded in the longitudinal end regions, wherein the narrow portions are adjacent to each other.