Given an edge-weighted undirected graph G = (V,E,c,w) where each edge e ∈ E has a cost c(e) ≥ 0 and another weight w(e) ≥ 0, a set S ⊆ V of terminals and a given constant C 0 ≥ 0, the aim is to find a minimum diameter Steiner tree whose all terminals appear as leaves and the cost of tree is bounded by C 0. The diameter of tree refers to the maximum weight of the paths connecting two different leaves in the tree. This problem is called the minimum diameter cost-constrained Steiner tree problem, which is NP-hard even when the topology of the Steiner tree is fixed. In this paper, we deal with the fixed-topology restricted version. We prove the restricted version to be polynomially solvable when the topology is not part of the input and propose a weakly fully polynomial time approximation scheme (weakly FPTAS) when the topology is part of the input, which can find a (1 + ε)-approximation of the restricted version problem for any ε > 0 with specific characteristic.