  We measured the pressure dependence of in-plane resistivity $\rho_{ab}$ in
the recently-discovered iron-based superconductor
Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$, which shows a
unique structural phase transition in the absence of magnetic ordering, with a
superconducting transition temperature $T_{\rm c}$ = 16 K and structural phase
transition temperature $T_{\rm s}$ $\simeq$ 100 K at ambient pressure. $T_{\rm
c}$ and $T_{\rm s}$ are suppressed on applying pressure and disappear at
approximately 0.5 GPa, suggesting a relationship between superconductivity and
structure. Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$ is a
rather rare example in which the superconductivity appears only in a
low-temperature ordered phase. The fact that the change in the crystal
structure is directly linked with superconductivity suggests that the crystal
structure as well as magnetism are important factors governing
superconductivity in iron pnictides.
