Temperature uniformity of a reaction liquid in a plurality of reaction containers of an automatic analysis device is maintained by a heat block. A strip-shaped heater heats the heat block, and 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. The strip-shaped heater includes a heat generating resistor that is heated by applying an electric current, an insulating film sandwiching the heat generating resistor, and first and second electrical feed lines that are attached to both end portions of the heat generating resistor and supply power to the heat generating resistor. The width of the heat generating resistor in both end regions of the strip-shaped heater is formed to be narrower than the width of the heat generating resistor in the other region thereof.