A method for predicting an effect of a tumor immunotherapy, wherein the predicting an effect of a tumor immunotherapy is detecting a patient for whom the effect of a tumor immunotherapy is beneficial, the method comprises step 1: contacting peripheral blood mononuclear cells collected from a patient who is a target for treatment of a malignant tumor with tumor cells indirectly via a bispecific molecule or a trispecific molecule in vitro, wherein the bispecific molecule or the trispecific molecule contains an antigen-binding domain that binds to at least one member of T-cell surface antigens and an antigen-binding domain that binds to at least one member of surface antigens of the tumor cells, step 2: determining whether the tumor cells that contacted with the peripheral blood mononuclear cells in step 1 are damaged, and said step 2 comprises the step of obtaining a value that reflects the tumor-cytotoxic activity by measuring tumor-cytotoxic activity of the peripheral blood mononuclear cells that contacted with the tumor cells, and the step of comparing the value that reflects the tumor-cytotoxic activity with a corresponding reference value and determining that the tumor cells are damaged when the value is higher than the corresponding reference value, and step 3: determining that the tumor immunotherapy is effective against the malignant tumor in the patient from whom peripheral blood mononuclear cells have been collected and measured for tumor-cytotoxic activity, when the tumor cells are determined to have been damaged in step 2. step 1: contacting peripheral blood mononuclear cells collected from a patient who is a target for treatment of a malignant tumor with tumor cells indirectly via a bispecific molecule or a trispecific molecule in vitro, wherein the bispecific molecule or the trispecific molecule contains an antigen-binding domain that binds to at least one member of T-cell surface antigens and an antigen-binding domain that binds to at least one member of surface antigens of the tumor cells, step 2: determining whether the tumor cells that contacted with the peripheral blood mononuclear cells in step 1 are damaged, and said step 2 comprises the step of obtaining a value that reflects the tumor-cytotoxic activity by measuring tumor-cytotoxic activity of the peripheral blood mononuclear cells that contacted with the tumor cells, and the step of comparing the value that reflects the tumor-cytotoxic activity with a corresponding reference value and determining that the tumor cells are damaged when the value is higher than the corresponding reference value, and the step of obtaining a value that reflects the tumor-cytotoxic activity by measuring tumor-cytotoxic activity of the peripheral blood mononuclear cells that contacted with the tumor cells, and the step of comparing the value that reflects the tumor-cytotoxic activity with a corresponding reference value and determining that the tumor cells are damaged when the value is higher than the corresponding reference value, and step 3: determining that the tumor immunotherapy is effective against the malignant tumor in the patient from whom peripheral blood mononuclear cells have been collected and measured for tumor-cytotoxic activity, when the tumor cells are determined to have been damaged in step 2.