An outdoor unit of a refrigeration cycle apparatus, the outdoor unit being connectable to a load device including a first expansion valve and an evaporator, the outdoor unit comprising: a compressor having a suction port, a discharge port, and an intermediate pressure port; a condenser; a heat exchanger having a first passage and a second passage and configured to exchange heat between refrigerant flowing in the first passage and the refrigerant flowing in the second passage, wherein a flow path from the compressor to the first passage of the heat exchanger via the condenser forms, together with the load device, a circulation flow path through which the refrigerant circulates; an injection flow path configured to cause the refrigerant to flow from a branching portion to the compressor, the branching portion being between an outlet of the condenser and an inlet of the first passage in the circulation flow path, wherein the injection flow path is provided with: a first refrigerant flow path (91~94) configured to cause the refrigerant to flow from the branching portion to an inlet of the second passage; a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intermediate pressure port of the compressor; a receiver disposed on the first refrigerant flow path (91~94); a second expansion valve disposed at a portion between the branching portion and an inlet of the receiver in the first refrigerant flow path (91~94); and a flow rate control valve disposed at a portion between an outlet of the receiver and the inlet of the second passage in the first refrigerant flow path (91~94); a controller configured to control the compressor, the second expansion valve, and the flow rate control valve; and a notification device configured to notify a user of information from the controller, wherein when a supercritical state is reached where a discharge pressure of the compressor exceeds a critical pressure of the refrigerant, the controller determines whether or not the refrigerant included in the circulation flow path and the injection flow path is insufficient, based on a degree of opening of the flow rate control valve. a compressor having a suction port, a discharge port, and an intermediate pressure port; a condenser; a heat exchanger having a first passage and a second passage and configured to exchange heat between refrigerant flowing in the first passage and the refrigerant flowing in the second passage, wherein a flow path from the compressor to the first passage of the heat exchanger via the condenser forms, together with the load device, a circulation flow path through which the refrigerant circulates; an injection flow path configured to cause the refrigerant to flow from a branching portion to the compressor, the branching portion being between an outlet of the condenser and an inlet of the first passage in the circulation flow path, wherein the injection flow path is provided with: a first refrigerant flow path (91~94) configured to cause the refrigerant to flow from the branching portion to an inlet of the second passage; a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intermediate pressure port of the compressor; a receiver disposed on the first refrigerant flow path (91~94); a second expansion valve disposed at a portion between the branching portion and an inlet of the receiver in the first refrigerant flow path (91~94); and a flow rate control valve disposed at a portion between an outlet of the receiver and the inlet of the second passage in the first refrigerant flow path (91~94); a first refrigerant flow path (91~94) configured to cause the refrigerant to flow from the branching portion to an inlet of the second passage; a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intermediate pressure port of the compressor; a receiver disposed on the first refrigerant flow path (91~94); a second expansion valve disposed at a portion between the branching portion and an inlet of the receiver in the first refrigerant flow path (91~94); and a flow rate control valve disposed at a portion between an outlet of the receiver and the inlet of the second passage in the first refrigerant flow path (91~94); a controller configured to control the compressor, the second expansion valve, and the flow rate control valve; and a notification device configured to notify a user of information from the controller, wherein when a supercritical state is reached where a discharge pressure of the compressor exceeds a critical pressure of the refrigerant, the controller determines whether or not the refrigerant included in the circulation flow path and the injection flow path is insufficient, based on a degree of opening of the flow rate control valve.