An evaporative fuel treatment apparatus comprising: a canister that adsorbs evaporative fuel; a vapor passage that is connected to the canister and that introduces evaporative fuel produced in a fuel tank into the canister; an outside air introduction passage that is connected to the canister and that introduces outside air into the canister; a purge passage that connects the canister and an intake passage to each other; a sealing valve that is provided in the vapor passage and that is configured to open or close a flow channel of the vapor passage; a tank internal pressure sensor configured to detect a tank pressure as a pressure inside the fuel tank; a pressure sensor that is provided in at least one of the canister and a region of the vapor passage located on a canister side with respect to the sealing valve, the pressure sensor being configured to detect a vapor pressure as a pressure in the flow channel of the vapor passage; and an electronic control unit configured to detect the tank pressure based on a signal input from the tank internal pressure sensor, detect the vapor pressure based on a signal input from the pressure sensor, and perform control to open or close the sealing valve, characterized by the electronic control unit being further configured to determine whether or not there is an abnormality in the tank internal pressure sensor, based on a change in the vapor pressure in changing over the sealing valve from a closed state to an open state, when the electronic control unit determines that an amount of change in the tank pressure in changing over the sealing valve from the closed state to the open state is lower than a first predetermined value set in advance. a canister that adsorbs evaporative fuel; a vapor passage that is connected to the canister and that introduces evaporative fuel produced in a fuel tank into the canister; an outside air introduction passage that is connected to the canister and that introduces outside air into the canister; a purge passage that connects the canister and an intake passage to each other; a sealing valve that is provided in the vapor passage and that is configured to open or close a flow channel of the vapor passage; a tank internal pressure sensor configured to detect a tank pressure as a pressure inside the fuel tank; a pressure sensor that is provided in at least one of the canister and a region of the vapor passage located on a canister side with respect to the sealing valve, the pressure sensor being configured to detect a vapor pressure as a pressure in the flow channel of the vapor passage; and an electronic control unit configured to detect the tank pressure based on a signal input from the tank internal pressure sensor, detect the vapor pressure based on a signal input from the pressure sensor, and perform control to open or close the sealing valve, detect the tank pressure based on a signal input from the tank internal pressure sensor, detect the vapor pressure based on a signal input from the pressure sensor, and perform control to open or close the sealing valve, characterized by the electronic control unit being further configured to determine whether or not there is an abnormality in the tank internal pressure sensor, based on a change in the vapor pressure in changing over the sealing valve from a closed state to an open state, when the electronic control unit determines that an amount of change in the tank pressure in changing over the sealing valve from the closed state to the open state is lower than a first predetermined value set in advance.