A fuel pressure estimation system configured to estimate a fuel pressure variable on a fuel pressure, which is a pressure of fuel in a supply pipe (53, 58), for an engine apparatus including an engine having a fuel injection valve (25, 26) and a fuel supply device having a fuel pump that supplies the fuel in a fuel tank to the supply pipe (53, 58) connected to the fuel injection valve (25, 26), characterised in that: the fuel pressure estimation system is configured to estimate the fuel pressure variable on a low-pressure fuel pressure (P flo), which is a pressure of the fuel in a low-pressure supply pipe, the fuel pump is configured as an electric pump that operates by receiving electric power supplied from a battery, and wherein the fuel pump is further configured to supply the fuel in the fuel tank to the low-pressure supply pipe, and the fuel pressure estimation system comprises: a storage device configured to store a first mapping that receives, as an input, first input variables including a pump variable on a state of the fuel pump, a consumption flow rate variable on a consumption flow rate of the fuel of the engine, and a property variable on a property of the fuel, and outputs the fuel pressure variable, wherein the pump variable includes at least a part of a pump rotation speed variable on a rotation speed of the fuel pump, a pump current variable on an operation current of the fuel pump, and a pump voltage variable on an operation voltage of the fuel pump; and an execution device configured to acquire the first input variables and estimate the fuel pressure variable by applying the first input variables to the first mapping. the fuel pressure estimation system is configured to estimate the fuel pressure variable on a low-pressure fuel pressure (P flo), which is a pressure of the fuel in a low-pressure supply pipe, the fuel pump is configured as an electric pump that operates by receiving electric power supplied from a battery, and wherein the fuel pump is further configured to supply the fuel in the fuel tank to the low-pressure supply pipe, and the fuel pressure estimation system comprises: a storage device configured to store a first mapping that receives, as an input, first input variables including a pump variable on a state of the fuel pump, a consumption flow rate variable on a consumption flow rate of the fuel of the engine, and a property variable on a property of the fuel, and outputs the fuel pressure variable, wherein the pump variable includes at least a part of a pump rotation speed variable on a rotation speed of the fuel pump, a pump current variable on an operation current of the fuel pump, and a pump voltage variable on an operation voltage of the fuel pump; and an execution device configured to acquire the first input variables and estimate the fuel pressure variable by applying the first input variables to the first mapping. a storage device configured to store a first mapping that receives, as an input, first input variables including a pump variable on a state of the fuel pump, a consumption flow rate variable on a consumption flow rate of the fuel of the engine, and a property variable on a property of the fuel, and outputs the fuel pressure variable, wherein the pump variable includes at least a part of a pump rotation speed variable on a rotation speed of the fuel pump, a pump current variable on an operation current of the fuel pump, and a pump voltage variable on an operation voltage of the fuel pump; and an execution device configured to acquire the first input variables and estimate the fuel pressure variable by applying the first input variables to the first mapping.