An object is to enable accurate calculation of the energy supplied to a cylinder member and enable properly changing the supply energy in accordance with the type of molding material. A molding-machine supply-energy calculation apparatus includes a high-frequency-current generation circuit including a coil (16) disposed on a cylinder member, a DC voltage generation circuit (31), switching elements, and capacitors (C1 to C4), and adapted to generate high frequency current through switching of the switching elements and supply the current to the coil (16); an electrical variable detection section that detects an electrical variable representing a state of a resonance circuit (SR2); drive-signal generation processing section that generates drive signals (g1, g2) driving the switching elements on the basis of the electrical variable; and supply-energy calculation processing section that calculates the energy supplied to the cylinder member on the basis of a voltage generated by the DC voltage generation circuit (31), the capacitance of the capacitors (C3, C4), and the electrical variable. It becomes unnecessary to take the loss associated with switching of the switching elements into consideration.