A foam body constituted of a 4-methyl-1-pentene-based polymer, in which one or more temperatures showing a maximum value of loss tangent (tan δ) of dynamic viscoelasticity, which is obtained by dynamic viscoelasticity measurement conducted under the conditions of a temperature increase rate of 4° C./min, a frequency of 1.59 Hz, and a distortion of 0.1%, exist in at least a range of 10° C. or higher and 100° C. or lower, and the maximum value of the loss tangent is 0.5 or more and 3.5 or less. Another aspect relates to a polyolefin-based foam sheet constituted of a 4-methyl-1-pentene-based polymer, in which the difference in Shore A hardness of at least one surface at different times is defined. A further aspect relates to a complex including a foam body constituted of a 4-methyl-1-pentene-based polymer and a member which is bonded to the foam body and is different from the foam body.